This is really not the first case that the love story is not the centre of the story and takes a massive backseat.
There are even stories where the main love interest of the protagonists isn't even the second most important character, that's actually really common in superhero stories. He's the second most important character in terms of screentime here though, and even then, he's a recurring character and nothing more, he doesn't appear for entire episodes or gets like one line or a small conversation.
Truth, but it goes far further than “not an ensemble”, if you look at Honey Lemon Soda, the story is from Uka's perspective and it's not an ensemble cast but Kai gets like what, 70% of Uka's screen time? This love interest gets 15% or something, probably less, and he's still the second most important character.
This is a one man show with recurring characters.
Because writing about a character one doesn't like isn't fun. The writer also obviously doesn't want it to become too much of a romance story, isn't all that interested in writing that, and consequently bad at it.