I think part of the problem, is some characters are written mostly as love interests for the MC, rather than characters in their own right with plans and goals they’re going to go after that don’t necessarily include the MC. (Can’t comment on Dragon Racer as I haven’t read it.This is just a general observation.) Not saying they’re all like this, but I do find non-RO’s often tend to be stronger characters and that makes them interesting making the push for characters that were never designed to be a love interest included. (See below as an example.)
The problem with this is because their design was not to be a love interest for the MC, they DO often have their own story arc that in some cases can come into conflict with being a continued love interest. I agree, if they’re not suitable for it and were never planned as such, they probably shouldn’t be written in as one, but it can be hard. I’ve had PM’s with detailed arguments on why I should include people (some of which I’ve said will not be romanceable) as RO’s. It’s great that readers are getting that into games, don’t get me wrong (thank you for being that invested in something I’ve written!), but it can put a lot of pressure on authors trying to make everyone happy to include them, but ultimately that can backfire if they’re destined to dump the mc/die/disappear for storyline purposes.
But yep, need to be a little forgiving on this front IMO, and just be mindful when asking for RO’s, if the author hasn’t included them, there can be a reason why and continued pressure to have them included can result in no one being particularly happy with the end result.