Yes there is a general trend that a new "market place" opens up. It could be adwords, or it could be udemy. There is then a race to the top/bottom where the marketplace becomes popular and crowded out. The "crowd" progressively gets a worse deal (except for the winners of the crowd) and the owner makes more money.

For example adwords:

1. Crowd gets worse deal: average bidder pays more for ads, hard to make a profit, might break even if you are lucky. Might be OK in a new niche if lucky.

2. Winners: people with sharp marketing teams who can bid on the right keywords and have an excellent sales funnel to take advantage. They can outbid the crowd and make a profit.

3. Owner: Google makes a tonne of money from ads of course:

Udemy:

1. Crowd gets worse deal: I saw a 80 hour course for $20 on there. Most are 20-30 hours course for $20. Course maker gets a fraction of that. 100's of similar course means the platform doesn't necessarily give you much traffic.

2. Winners: Some people sells thousands of units of their course on these platforms. Again those with good funnels to get them to buy off the platform probably win (I am guessing).

3. Owner: Udemy does well.

Same applies to the app stores!