According to the notes, PBS had its funding gutted and they could no longer afford to make new episodes, so HBO stepped in back in 2015 and offered to fund the show. It will air new episodes and after a few months (I'm seeing six months and nine months) the new episodes will air on PBS Kids.

So it's not being out behind a paywall permanently, it's still available just a little late. It was either this or cancel the show.

Not ideal but blame the politicians that slashed PBS funding.