Why would we kick out inactive players
Because they are warned that after a period of time they will lose their house. It's the ingame ToS. Also, iirc, they get back 80% of their investment and most of their furnishings.*

Then also have all these now vacated plots with interested buyers, but restrictions prevent their use?
Because they consider the priority should be FCs. A FC can "house" multiple people who can use rooms (That work just like apartments). Who (for the most part) will share the building (just like apartments) with the added benefits of Workshops (and other due experiments) that would benefit a group (just like apartments).