Because it has cute girls/college students in it who wear stylish clothes - which is why I'm watching it too, but I could do without MCs "problems".
edit: what I'm saying is, the premise of this show is that MC can't get a girlfriend and finds love while doing this rental stuff out of spite etc. yada yada. So sure thing, MC is going to be a bit of an introvert, but I doubt the people who are like that in real life would act like he does in front of a potential romance, especially when he actually doesn't even want to be that way.
Like, he would look away awkwardly, everyone is probably able to tell that he feels sad whenever he thinks about his ex-girlfriend and doesn't value himself as much due to what has happened. But that is a completely different level, especially since, as mentioned, the reason is so "small". It doesn't look like he suffered a life of solitude, he has friends (good friends) who seem rather normal guessing by what has happened in the last episode.
When you look at the first two episodes, where MC even gets angry about being "played" by the rental-girlfriend, you get a completely different picture about him too. It's just weird when he goes into complete shutdown-mode like that