I think it has to do with things like possible scandals, how it will negatively affect an idol's career, and how it's not as easy to accept in their culture and society. And Mikura was playing dumb but Yori showed that he has an idea of how Mikura feels for him (when he called him out about how Mikura had kissed back seriously) but he's going to prove himself so he's not heartbroken or feeling rejected. And Mikura showed that he is perfectly aware of how he feels for Yori, he just doesn't want to complicate Yori's career and he doesn't yet have the resolve to act on his love.
Ah. Yes that makes perfect sense. Didn't think about that.
After they kissed I was like "don't be an asshole. Don't be an asshole.", aaaaaand he was a bit of an asshole. *sigh*
It hasn't really made it clear WHY he wants to distance himself. Obviously he thinks of Yori as more than "just an idol". They are both adults and have the same feelings sooooo why?
Also this scene http://www.mangago.zone/read-manga/koi_ni_wa_mukanai_shokugyou/uu/m_v-1-chapter-5/pg-11/ ...(whoops for some reason the link takes you to page 11 but it's page 10 that I'm talking about)...... Like uh huh clearly you don't love him, you just conveniently picked a smoking spot right next to a big ass billboard with his face on it.
Also Miruka is sexy as fuck.