Both their functionings are complex, so people can get impressed. But for both of them, all the complexity is inside the device and there isn’t much to put together; and the way they hook up to your house is really simple.
Why YSK: so you don’t live too long with a broken toilet or garbage disposal, thinking it will be too hard to replace. Those two are some of the simplest things to DIY.
Also, a lot of the stuff in a toilet can be replaced, so you don’t necessarily need to spend hundreds of dollars on a new toilet when maybe a 50 dollar gasket kit will do the trick.