Amazon has free returns for now as only a tiny minority uses that as an option. Also returns work largely if there is a defect or you genuinely bought a wrong product(Like a wrong shoe size).

If most users start doing returns, they won't be free or even possible, given how much logistical nightmare that will be.

Beyond all this, that turn around time to buy a single product will be high.

Stores offer a good middle ground, and you can get a good hold of things before you actually make a purchase. I'm not saying toy purchase or any other purchase online will go down, but there will be a lot of buying will be waste.