I mean they kind of do. Most of the time I would hand wave away any company offering gift cards or credits, but Steam has created an economy / structure that I think warrants mentioning here.

I have sold a few items on Steam because I don't care about cosmetics in games. I'm also lazy and because of that "sat" on items for a while that appreciated. I mention this because Steam credit is very fungible: it can be easily converted.

Steam also makes it very easy to redeem credit, gift, etc.

I believe you can buy Steam cards at most places Xbox cards and similar are sold as well.

Also in the early days of Bitcoin buying and selling of digital Steam assets was one of the most popular things.