The more advanced the math, the more steps and effort goes into solving a problem. I think that makes it harder to gamify. You get to the point in calc where a problem might take several pages to do.
What I would really like is daily problem/brain teaser type things. The ones I see online are either extremely easy or intentionally written in a confusing way to get engagement.
I haven’t tried Brilliant so I don’t know how good it is but that claims to do what you want.
I don’t think there’s as much money in it as you think there is. The students who struggle with math aren’t going to look for that type of resource - they just try to struggle through. The students who are interested already know about resources like Organic Chemistry Tutor and Paul’s Notes.
If an interested dev does stumble on this thread, I do frequently help students with math and would love to consult for money lol