I think you have it in reverse, Tamers' SU romance arcs are very drawn out and have a lot of time to let the characters marinate. This is why we care when the character cares.
All you really have to do for comparison's sake is ask what the hell Braeburn did besides kiss another man to try and make you like him. Knuckles and Sonia are both involved in the earliest Tamers shipping stuff (yes it even predates Bardonic, at least on his Youtube channel) but you could easily come up with a bunch of reasons why those two are fun to watch. The same of true of basically everyone in his SU content (with one exception, but that's another discussion.) Knuxonia could stop being involved in romance plots tomorrow and you'd still get enjoyment out of their personalities and what they do in various episodes. Meanwhile Braeburn and Soarin exist for shipping, plain and simple.