Guys help me to understand?

Guys for one to two years a guy have matched me on tinder like five times and I find him handsome, I followed him on Instagram in June (His account is private so he accepted me) but he hasn’t follow me back but he like my tinder profile fire Fifth time in September or October.
so I liked his new Instagram picture two days ago and he watched my story few minutes after, I did a little spy lol and I saw he literally follow every girl except me!!
so I’m asking why? I can tell I’m prettier than many of them but that’s not the problem, the problem is why doesn’t he follow me back?
Guys help me to understand?
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