First of all, disadvantaged and less-fortunate children still have access to SS; PBS still airs the show for completely free on a nine-month delay system after the new episodes are initially released on HBO, so it's not like it's exclusive to rich people.
Secondly, SW has had a turn-over in their staff in recent years, and unfortunately, a lot of their higher-ups have previously worked for such media conglomerates as Viacom, so that has a lot to do with the far more corporate approach SW has been handling not only the business aspect of the Sesame brand, but the decisions they've made with the actual show itself.
Lastly . . . I mean, a little part of me does leave a poor taste in my mouth that this is the direction they're going in; not everybody has HBO as a cable channel, let alone their streaming service - especially the aforementioned disadvantaged and less-fortunate, so from that perspective, yeah, I can see where you're coming from. On the other hand, the move to HBO actually saved the show in the long run: PBS funding is being bled-dry . . . now more than ever as Trump's so-called "Administration" is trying to cut funding for PBS altogether; SS was on the verge of collapsing if they remained with PBS. Now partnered-up with HBO, funding and financing is no longer a major concern of theirs, so it can continue to thrive and prosper. And, again, the show is still aired on PBS for all to see, the new episodes just don't air until nine months after they've aired on HBO . . . all things considered, it's not a bad deal at all.