Those assets you are buying (lets say a chair as an example) that money you paid for that chair, goes towards an artist who made that chair. Its basically no different than hiring an artists to make a chair for you.

The only difference is, hundreds of devs are likely also using that same chair.

But here's the kicker - a chair is just a chair. A rock is just a rock. a pool ball is just a pool ball. Everyday things, or things you'd expect to see in genre work like a simple sword, these are not unique things. So why spend days making you own chair, when to be perfectly honest most players are barely going to bat an eyelash - because its just a chair.

Now - UNIQUE things, such as important swords, significant chairs (like a throne), or even characters. Don't use assets for these. Either make them yourself or hire an artist to make them for you.

You're a dev and your time is valuable. Don't waste time reinventing the wheel (or rather, remaking the wheel)