Initially the green hill reuse was'n that bad, seeing it as an unlockable completion reward in adventure 2 or as a stage in a spinoff was nice. It was also cool to see in smash bros brawl.
It became a problem for me after generations, which is imo the last time sonic team should have reused old stages in the scale they did because it was a celebration of the whole series. It started getting grating when the main series game right after generations (forces) used green hill and chemical plant again, both of which also made an appearance in sonic mania right before they did in forces. Hell both of those stages even sneaked their way into sonic frontiers.
i can excuse the reuse of green greens and 1-1 with 2D mario games and kirby games because not only do the both tend to follow a pattern with their level themes (grassland, desert, ocean, forest etc.) those games also tend to be really good. Where as the level themes in sonic games can get really out there so i feel really bummed out when in place of something new and interesting they have another green hill, the quality of the sonic games also can radically shift between titles so i think it's important to actually make your game feel interesting if there's a chance that it isn't going to be that good.