Everyone has seen a card trick, just like everyone has seen a movie.
Just like movies, there are plenty awful ones, and a few outstanding ones.

Card tricks can be boring for few reasons. 

  1.  Everybody does them, and most people who do them do them badly.
  2.  Many card tricks are long, complicated, repetitive, and difficult to follow. 
  3.  They are predictable.  Most card tricks laypeople are familiar with have the same plot. 
    A card is lost, then it is found (by the magician).

Regarding 1., most people do a card trick badly simply because they believe the secret of magic is in knowing the secret to a trick.  There are many important factors that can make or break a card trick, including misdirection, technique, humor, and plot (hint: the plot must be better than, "The card was lost, but I found it."

Regarding 2., I think most card tricks are too long, too convoluted, and hard to follow.  Why?  Most people performing a card trick spend 90% of the time on the discovery and 10% (if that) on the revelation.  In other words, they have some method that may take take minutes just to find the card.  This can be boring for everyone except the performer.  
One example is that chestnut, the 21 Card Trick (there are, in fact, two tricks often called by this name, but I'm referring to the one that sucks...the one you've probably seen). 
After the card is selected and returned, the deck is dealt into three columns of seven cards. 
The performer asks a question, picks up the cards, and then it gets even less interesting. 
The cards are dealt into three columns of seven cards--again. 
The performer asks another question. 
After this--finally--the performer reveals the card (in an interesting way, it is hoped).

I do confess that the first time I saw this trick, I loved it.
Admittedly, I was six years old.  I was nonplussed how my card could be found.  I knew he had not seen it, and I knew it had been utterly lost among the other cards.  At the time, that was enough for me.

Now when I see that, I fight a yawn.  To perform card tricks entertainingly, not only must you know how the tricks are done, but how to do them.  There is a huge difference between the two.  Knowing the secret of a trick is not the same as knowing how to perform that trick--and knowing the secret to hundreds of tricks is of little value unless each can be performed gracefully.

Most of the performance of that little charade of 21 cards is taken up by the dealing of cards into rows and columns.  All this so the performer can discern the card.  A topflight magician can discern the correct card within mere seconds, and he is done with that necessary but not sufficient phase of the trick--then he can choose to spend as much or as little time as he needs on the presentation.
Why not instead learn a better, quicker, and more invisible method?
There are many methods that grant you the knowledge of the chosen card in seconds, not minutes.

One may argue that all that time can be filled up with dramatic patter, but that is a cop-out.
If you are restricted to that method, you are restricted to your performance being ruined amid interruptions.  If your dramatic patter is essential, all the more reason to choose a better method--that way, you can focus more on your theater and less on your clumsy method.

Regarding 3, fortunately, most professional magicians--even the bad ones--are knowledgeable enough not to stop at simply finding a card.  One of the best card tricks I do--possibly the best--has no element of this "finding a lost card" business; furthermore, in all the tricks I do where I do find the card, the revelation is far more arresting and memorable than the discovery.  By "revelation," I mean the manner in which I reveal that I know the card.  It may appear in your pocket, it may appear folded up inside an ice cube in your drink, it may appear under your drink, it used to appear folded up in my mouth but I don't do that anymore because I do feel it's in bad taste.  At times I'll have two people choose a card, one for each of them, then remember their cards, then have both cards switch places so that the first person is holding the second person's card and the second person is holding the first person's card--I'm sure you'll agree that this is more surprising than my finding a card.

All the above still doesn't answer the question, "Why do magicians do card tricks?"
Why don't you see a magician doing three pencil tricks, followed by another magician doing his best pencil trick?  Or umbrella tricks or thimble tricks?  

Is it because there are four suits in a deck, and four seasons in a year; 52 cards in a deck, and 52 weeks in a year; 13 values, and 13 phases of the lunar cycle?  Surely this must be the reason magicians like playing cards.  


For your information, thimble magic used to be almost as popular as card magic; but nobody knows what a thimble is these days.  Let's ignore thimbles for now. 

Magicians do card tricks because of the following:

1.  Versatility.  With one deck of cards, I personally could entertain and astonish a group for hours.  There just aren't that many umbrella tricks (plus, I'd rather walk into a party with a deck in my pocket than an umbrella).

2.  Audience Familiarity.  Any mediocre trick with a familiar object is ten times better than a great trick with an unfamiliar object.  Everyone knows what a deck of cards is.  The same could be said of coins (which explains why coin magic is almost as popular as card magic).

3.  Practicality.  There aren't many props as small as a deck of cards that can hold an audience spellbound for several hours.  As I have advanced in magic, I've come to appreciate the value of showing up to an event without any props and presenting.  When my point of contact asks, "Do you need anything?" I'm very comfortable saying, "No." 

Now you know that there are three reasons magicians like playing cards.
There will never be a fourth reason.
You also know that card tricks are like movies: there are good ones and bad ones.
If you know a bad card trick, please be sure to keep it close to your vest.