Sports franchise values are increasing, in general, because they're artificially limited in number (there are only 32 NFL teams) and specifically because of (a)

Sports franchise values are increasing, in general, because they're artificially limited in number (there are only 32 NFL teams) and specifically because of (a) increased rights fees, (b) rising value of local broadcast deals, especially in large markets like LA and NY and (c) taxpayer-subsidized stadiums. At the same time, there's more competition than ever for the national broadcast deals which is why ESPN had to overpay for its NFL and NBA deals. And those broadcasting rights keep decreasing in value as each league gets to sell its product multiple times (for the NFL there are games on broadcast networks, ESPN, streaming-only games, NFL network games, Sunday Ticket, and RedZone). ESPN is in a bad spot since they have to have NFL games, because even though their Sunday Night Football deal only lets them air one (usually terrible) game a week, it means they get to fill their network the rest of the time with NFL highlight / analysis shows.