These are the common reasons. You may have another!
1. Portability
2. Inexpensive
3. Easier to Learn
1. A regular (some erroneously call them "real" as if "electronic" was the opposite of "real") acoustic piano, the smallest I could find, weighs in at 300 HUNDRED pounds. My very expensive keyboard weighs a whopping 24 pounds. Yet it does things an acoustic never thought of doing. See the next points for that.
Also, an acoustic piano is large (as almost everyone knows) while keyboards are much, much smaller.
Guess which one is more "portable."
2. Inexpensive: Sure, you can find a used piano, but who can say how valuable it actually is. If YOU can, then more power to ya! Decent keyboards start at $100 new and actually sound great. Try one out NOW if you don't believe me. And that basic keyboard is good enough to get started. You can always upgrade later if you would like to.
there are actually two other ways that a keyboard is cheaper than an acoustic piano:
A. The cost of lessons, and
B. The cost of the built in stuff.
Let me explain!
A. Lessons cost money, cause there is no way I know to learn for free online. Yeah, a ton of people claim that they can teach you but I'm not buying it. There's too many bad habits you can fall into, even with Skype.
Since you have to take some lessons (and good ones can be expensive,) it makes sense to not take too many. An acoustic piano is hard to learn, typically requiring many years for an adult to master it, let alone a child.
A keyboard is much easier. The other day a ex-piano student who had been learning a tune every month, asked me for SIX tunes in his keyboard work. How about that?
Also, you won't have to pay as much gas for visiting the instructor, either!
for one reason or another
B. The built in stuff:
Keyboards never need tuning. Acoustics need one per year. If you don't do that, you risk having the acoustic "not hold a tune." Yep, many do just that, not tuning their instrument very often (if at all.) Eventually, it sounds like an old-western bar piano.
Also, have you heard of a "metronome?" This is a very useful device to assist learning tunes. Keyboards have these built in, but not so acoustic pianos. You have to buy one.
C. Easier to learn - I referred to this above, but electronic keyboard is much easier to learn. Sorry, piano teachers, but I suspect that you simply want (for one reason or another) your students to "stick around" a long time. If so, then I suggest you make them into your personal friends.
