The stations are *hoping* for a revenue stream in ATSC 3.0. Meanwhile, TV manufacturers mainly just see added costs, not additional profits/sales.
And we don't know that MVPDs (pay TV distributors) are going to pay anything more for the right to carry stations' 3.0 signals with enhanced picture and sound quality. (As you say, a big majority of Americans watch the broadcast nets via pay TV, not free OTA.) Although, for that matter, stations don't necessarily even have to broadcast in 3.0 to offer enhanced feeds to MVPDs. Many NBC local affiliates, including ours here in Nashville, did that very thing during this summer's Tokyo Olympics when they transmitted an alternate 4K or 4K HDR version of their primetime feed to Comcast and YouTube TV. I see no reason why we won't some more of that happen with pay TV systems capable of doing it (i.e. managed IPTV and OTT systems, probably not QAM or satellite) and such developments can be completely separated from ATSC 3.0.
One of the big revenue streams from 3.0 is supposed to (eventually) be data-enabled broadband-delivered targeted ads for those viewers who have their 3.0 tuner connected to the internet. But Comcast, Charter and other pay TV operators already have their own targeted ad platforms and I can't really see them letting the broadcasters run their own ad platforms through the pay TV operator's STB/app. Everything online is always about controlling the UI, collecting the user data, and handling the targeted ads.