you can run playdate games on the desktop using the emulator included in the free SDK. It won't be as fun as running it on an actual device, but nothing stopping people from actually messing with making playdate games without a playdate.
yeah if you're aiming to make a proper professional game with aims of making profit... the playdate probably isn't the way to go. But then I recon that's part of what makes it an awesome platform. It hasn't been captured by capitalism yet.