Netflix is much more mainstream then what you are giving it credit for.
I'd argue the same thing about HBO, considering how many decades its been around, but as pointed out across the internet - and even this forum - apparently there's still a lot of people out there who
don't have HBO, let alone cable. That's where the comparison comes in: not everybody out there has Netflix, let alone internet access; this is why a lot of people have been making a big deal about SST's move to a cable TV subscription service when it was always meant to be an easily accessible show for kids (particularly lower income households) to tune into to watch (again, despite PBS will
still get the new episodes nine months later); it's a similar thing with THE MUPPETS, if they were wanting it to achieve a level of mainstream success like a lot of other network shows, moving it to an internet subscription service seems like an odd route to go.
Like Colbynfriends said, there are those out there who have only TV, and those out there who only have internet/streaming services. Streaming may be the future, but it's not there yet, and the number of people or households out there who still have broadcast TV still outnumber those who have only streaming services. Streaming services may be catching up, but there's still a ways to go.