Only the MC can communicate with them, the rest can't. For everyone else, they saw them just like horse, intelligent creature but still an animal. So they treat them pretty much how we treat horse irl, some are friendly and good with them and some are cruel and see them as nothing more than mere tools to be used and disposed of
This doesn't make sense, though, if it's commonly understood that dragons can understand human languages. Horses can't, a dragon would be both much more capable than a horse in basically every regard and also much more easy to train, command, and take care of due to being able to understand humans. This would naturally result in humans treating them like intelligent pets or work animals and not like simple tools, because they aren't simple tools, and treating them like pets results in happier (and therefore more amenable) dragons and higher efficiency, and a guild like Lindwurm would never be able to outcompete one that treats dragons like pets. It's a problem with the world building that dragons are treated so poorly, this would never happen, especially not when dragons are so commonplace.
This is all aside from the fact that humans tend to anthropomorphize everything, and would naturally come to treat any animal that they could have a friendly relationship with as pets. I mean, really, how many people talk to their pets despite knowing fundamentally that their pets cannot understand human languages? This effect would be even more pronounced for an animal which could understand them, so on every level it's a huge problem that the relationship between humans and dragons is so poor.
