I don't use D&D Beyond, so I'm not very familiar with it, but isn't it a platform entirely built around recurrent spending? I'm not sure what benefits subscribers get, but I've seen people talking about subscriptions, so I know people do subscribe. I think that they offer D&D Beyond versions of books for sale, packages of game elements from those books (like spells or classes), or the same sorts of things a la carte (like individual feats or backgrounds). I'm assuming they sell other things, like DM tools or fancier virtual character sheets or whatever.
All of that is recurrent spending, and since WotC spent blockbuster movie money (~$150 million) to buy D&D Beyond, all of that recurrent spending goes to them now. So, while it may be true that none of your recurrent spending goes to WotC, plenty of recurrent spending does. That is despite the existence of the OGL.
But that's not all. WotC are currently in the process of creating their own proprietary VTT, which will not only have graphics beyond what any other VTT will be able to offer but will also enjoy official support. It's going to completely dominate the market and make WotC a ridiculous amount of money. The OGL is not really a meaningful impediment to that.