There's a LOT of fog and confusion here, especially because so much has changed in the way the business works in recent years.
May I try to clarify?
"Must carry" has one very specific meaning in today's regulations. It is one of two choices that every full-power TV station has to make every three years. If a full-power TV station chooses to invoke must-carry, the cable and satellite providers within that station's DMA are required to carry that station's main (x.1) program stream, usually on a low channel number. No money changes hands in that scenario. This choice is thus usually made by stations without big 4 network affiliations.
The other half of the choice, the opposite of "must carry," is "retransmission consent." Stations that choose retrans consent give up their automatic must carry rights in exchange for the ability to negotiate with cable and satellite providers to charge them for the rights to offer NBC, ABC, CBS, Fox, Univision, etc. to their customers.
Cable companies cannot cherry-pick affiliates from outside their DMA to offer to their customers except in very specific circumstances where a system has historic carriage of out-of-market signals. Each local station (or really the group owners who dominate "local" TV) now has specific contractual terms with their networks that license them to provide network content only within their own DMA.
This has all changed dramatically within the last decade or so because of an underlying economic change in how local TV operates. Local stations no longer receive compensation from their networks to carry network programming, as was the case into the 1990s. The current scheme is "reverse compensation," in which the local station pays the network for the programming.
In an environment in which local advertising sales are plummeting, how do local stations survive and profit? That's why retrans consent is so important. It has become the largest source of revenue growth for the companies that own local stations, which in turn is driving consolidation, because it stands to reason that a Nexstar or Sinclair or Gray has maximum leverage against Spectrum or Comcast when it can pull hundreds of stations off the platform at once.
How much has it changed? At least based on some recent FCC filings, the average cable bill now includes close to $20 a month in retrans for local stations, a number that was about $1 a month as recently as 2011. Consumers can't opt out of local channels and the price tag that goes with them. All they can do is switch providers (if choices are available) or dump cable/satellite. And the OTT streamers (YouTube TV, Hulu with live TV, Sling, etc) also include retrans consent fees, the only difference being that those retrans negotiations are done directly with each network on behalf of its affiliates. There's also no must carry for the OTT services.
Does that all make sense in the context of 2025? Even a knowledge base from a decade ago doesn't really help to understand the industry as it goes through the most dramatic changes of any of our lifetimes so far.