Nothing special about the 20% proportion, just that it's proportional to a number which results in perverse incentives.
If the percentage is higher than the unconstrained optimal margin then the cap has no effect. There's no new pressure introduced yet.
If the percentage is lower than the unconstrained optimal margin then the only incentive is to increase the cost to raise the cap until right at the point demand decreases enough that any more cost would actually result in less total revenue. Because medical care is often very inelastic, that'd could quickly be a lot of cost inflation even for just a few percentage point constraint off the optimal margin. This is the part you're highlighting, and that makes sense.
The main counteracting force to this would be that a single insurer does not (theoretically, at least) set the cost of care directly on their own, they (theoretically, at least) compete with each other to negotiate the best care rates to have the most consumers go through them. There are several things which practically get in the way of that though, like how often you can actually change insurance plans or how competitive the open insurance market is (if you even have multiple options, some states only have a single marketplace option) vs just sticking with whatever your work offers.
Between all of that it is where comes back to the common refrains of "and that's why we need to go to a single payer system without profit as the main goal" and "and that's why we need to get rid of the ACA and let the market handle optimal profit naturally". Everybody can't seem to agree which way to go, just that they don't like the current way. Ironically, these approaches effectively map to the 0% cap (single payer, no profit focus) or the 100% (no ACA cap, free insurance market) interpretation options I originally listed.
I'm sure there about a billion other nuances not covered or thought about in this... but at least the comment parses now!
I firmly believe that was a poison pill put in the bill to try and eventually push insurance prices so high that Americans would acquiesce to single payer.
The alternatives are the bill’s authors were so stupid they didn’t see the negatives to that action, they thought it would play well to voters and the rest be damned, or the some big medical players got it put in - which would be risky, considering option A.
But yeah, with that in place they have no incentive to pay out less - they simply can’t have it raise higher than their competitors too quickly.
I feel like Republicans would have made a bill just to get rid of that one portion but the voters would hate it so much they can’t because people’s grasp on economics is too simple.