It has happened to me so many times where a game that I love fails to ever get a sequel (either that or it's taking forever to make one), the Rollercoaster Tycoon and SWAT series just to name a few. I'm almost certain there won't be another RCT but I think the Dev are still working on SWAT 5 or at least some kind of follow-up to SWAT 4. Any others out there that you guys can think of?
They pump those tycoon games out, so I wouldn't be surprised if rollercoaster got a sequel. Sadly, most of them are shovelware. SWAT 5 could be cool. I've never played any of them except for 4 though. I wish Bioware would make more Baldur's Gate games (instead of having other companies making those terrible Dark Alliance games). Its too bad that Baldur's Gate 3 was just compacted into an expansion pack for BG2 instead of being a full release (though it did end up being longer than most full games.) It was also a bit too hard. I've played through the entire series about 6 times, but never beaten the last on without cheating. In the final game, you have to kill the strongest five of your siblings. Not only are the areas to get to them nearly impossible to get through, they are practically invincible (other than the first one, which is scaled to your group's average level and the last one, who is surprisingly weak).