I feel like this is the main reason more apps don't offer an ad-opt-out as an IAP or buying a license or whatever the format might be.
The users most likely to go for it are the ones with the highest disposable income, i.e. the people most valuable to Advertisers.
Users with high DI * fee for removing ads < value of users to advertisers lost * users with high DI
Basically meaning that the revenue gained from allowing removal of ads would devalue their user pool in terms of advertising revenue so much that it's a net loss, even if they gain reputation with the users and possibly attract new ones.
This is just my theory though.
It's not just about losing 'reach', if only a few percent of people bought the opt-out that would probably be a minimal issue. It's also about who buys the opt-out; the people who can (and would) afford to do so are presumably wealthier than average and help justify ad sales more generally. I don't know the exact breakdown, but presumably it's a power-law situation. If you're the kind of consumer who could conceivably buy a truck through a Ford ad, how much more are you worth than everyone else? 2x? 10x? 20x?
(Of course, the kind of consumer who deeply dislikes ads is probably less likely to click them regardless of wealth. So maybe charging the ad-block contingent a flat rate would actually work out?)