There's a certain kind of naïveté that thinks "running on Broadway" = "winning." That's not really how it works. And for the record, I LIKE the Heathers musical, but I don't think Broadway would be a win for it. It just had a West End run, it's one of the most commonly produced musicals at regional, school and community levels, it has a proshot and TWO successful cast recordings. It's Tiktok famous. Hell, it has its own Riverdale episode.
What does a show in that position gain from being on Broadway? Literally nothing- in fact it probably loses. Broadway is expensive, and it would create a freeze on those licensing fees around the East Coast, which I'm pretty sure are more lucrative than the Broadway nut would be. And they aren't going to do a new proshot, and likely not a new cast recording. So the safest and most financially sound thing for the producers and rights owners is to let the Heathers machine run and not try to mount a flagship production: it's not an award bait show, and it's already achieved just about every goal a musical can achieve in terms of ACTUAL success, not just imaginary prestige.