Why did children's parties evolve from being held at home most of the time to being held outside the home?

When I was little (mid 1970’s), kids’ birthday parties were almost always held at home. I remember planning with my mom, what we were going to serve, the cake (she made it, not from a bakery), the games we were going to play, what was going to be in the “looty bags.” My friends’ parties were all similar. This was a solidly middle class, suburban environment.

Fast forward to the present time: little kids’ birthday parties seem to be almost exclusively outside the home – bowling alleys, Gymboree, local supermarkets and restaurants, craft places, athletic places – everywhere except the child’s home.

How and why did this come to be?