As a guy whose favorite movie of all time is Ghostbusters, I feel what this thread states on a personal level. But I do bring two sincere reasons why Ghostbusters the franchise sputtered out:
1) The franchise forgot it's a relatable, grounded comedy: people are already pointing this out, but the revival has this "reverence" for the old films that really miss that they were meant to just be workplace comedies with a coat of sci-fi painted over it. White-collar academics forced to go blue-collar entrepreneurs, with all the business woes that attend it from finding an HQ to bureaucrats on your ass. Now the series is about STAKES and EMOTIONS and all that heartstrings crap. It's meant to make you laugh and enjoy cool action scenes blending the working-class with the spooky.
2) It wasn't really meant to be a franchise: this is ironic as this has low-key been proven wrong in two forms: the Real Ghostbusters cartoon proved the concept works as a bust-of-the week series, and for once the FANDOM is right on the money: you could've stretched the movie side out with the concept of franchising (as the game in fact showed Rookie did, and IDW comics cleverly joked his group was doing better financially than the goddamn OG ones!). Even Girlbusters could've easily had a sensible connection and avoid being a reboot via the girls wringing out franchise permission from the retired OG Ghostbusters only to conveniently run into a new batch of ghosts and the incel villain making himself into a demonic entity as shown. But no, for some reason they just let the group fizzle out in-universe for decades, nothing being done with busting at all, until Egon's descendant finds old equipment and... yeah. The heck?
I love Ghostbusters, and GB2 in retrospect is a workable, enjoyable sequel (and far better than a lot of sequels, or movies in general, since), but this is a franchise that frankly speaking wasn't meant to be one at all in the long run. It should've remained behind as a beloved part of the 80s.
