They’ve lost fans who would watch if it was on tv, but won’t go out of their way to pay. YouTubetv is on pace to be the third largest by the end of the year. The Nats aren’t on YouTubetv. Other carriers are requiring higher tiers than they did for MASN. The nats will be a great case study on what happens when you make an ambivalent fanbase pay to see games. I’m guessing it won’t be pretty
This is a problem across MLB, and one that we've been talking about and could see coming years ago. YTTV has almost no local sports channels, and services like that are probably not the future of TV anyway. MLB's best bet is to get as many games as the can on a streaming service like ESPN or Netflix without an up charge. They hurt themselves by caring about the declining carriage fees too long. You are right though, relying on fans to pay extra is not going to be a good long term strategy for keeping fans and needs to be resolved across the league.
All in all, as consumers we're in a better space. MASN wasn't free, and it's funny that millions of subscribers (obliviously?) accepted paying $60ish per year for the channel whether they watched it or not. It's funny that it's a hard sell to get fans to intentionally pay $50/year.