1. One of the reasons may be todays lifestyle of constant moving about. Pianos cost a lot of money to move. Sometimes more than the piano itself cost.

2. Electric pianos today with their weighted keys and being touch sensitive are a viable alternative. They also sound pretty good.

3. I don't think most people realize how reasonable a spinet piano costs. Often on par with a guitar.

That said my mom was a concert/jazz pianist and my first piano lessons were on a Steinway baby grand and my first organ lessons were on a Hammond C3. Even with that I picked a guitar as my instrument of choice.