There is no lack of competition. They are just bad in obvious ways. I’m not saying it’s easy to take on a giant like Steam, but Epic for example is exactly the kind of company and amount of money that could. They didn’t, and it’s not because of the library effect. They simply went with the seemingly easiest way: pissing money on the problem (securing timed exclusives and free games). There is so much they could do to make the client and their service better, but they don’t. So no, it’s not a monopoly.