A lot can be and has been said about the things sadly left out from SwSh, but this one was a particular slap in the feels. It practically represents the total erasure of an aspect of the community. It's not a part of the community I was particularly engaged in (I don't think I've ever beaten, or for that matter even reached, a facility boss in any Pokémon game), but it felt good to know it was there and that there were people who had fun in other ways than I - like how I had fun in other ways than them. The mere existence of more stuff to do made it feel like the game would always have something new to discover. Another milestone to pass, should I decide to take the challenge.
For instance, I never completed Pokéstar Studios, but I always knew it would be there to provide several hours more of content if I chose to go into it. Same with Contests or Musicals or PWT or what-have-you: things I never really got around to, but whose existence made me think higher of the games anyway. I didn't always take the option to engage with these features, but knowing I had the option made the games feel rich in content, a feeling that probably made me enjoy them even more. I still think of B2W2 as games with more content for me to find, should I ever choose to take them down from the shelves. I don't feel like I've seen everything they have to offer.
But in SwSh, the Battle Tower is essentially meaningless, and there is no "perpetual challenge" in-game anymore. An option I won't have. Not sure if I would have taken it (my record Battle Tree streak of zero suggest I wouldn't - but on the other hand, that was mostly because prepping for the Tree would take way more time than actually playing it, which this generation seems to have simplified greatly), but I would know the option was available. And now I know it isn't there. It's one less thing for the community to talk about, and it feels like something is lost.
Game Freak probably changed the Battle Whatever because their data suggested few people ever bothered to chase streaks in the endless modes, but I think many players still cherished that feeling of having the option. Few players ever interacted with every bit of content the games have to offer, but each bit of content still had its fans, who would think "these games have a great adventure, this feature I really like, and a bunch of other things too!". Removing options like this makes the games feel poorer even for players who didn't play the Battle Whatever. It would be like the developers limiting the size of a Minecraft world to 5x5 kilometers because few players ever venture further than that from their home base. Dragging the borders of the world close enough that you can see them creates an inhibiting feeling that "this is all there is", taking away that potential for limitless exploration. Even homebound players would be upset about that change.
There's VGC, if you want to bother with that. If not, well, what you said, but you are also expected to be hyped for the next game in the series when that time of the cycle comes along. At times, I get in a cynical mood and wonder if Game Freak purposefully avoids designing for longevity, as that would make it harder to sell the next game in the series.