Why would my gf keep changing profile pictures to get more likes?

[FSBB]

Ok, this is one weird habit of my girlfriend. She is seriously totally normal but is a total like whore on Facebook. Like I don't get it. She is not materialistic at all, but when it comes to Facebook, she does two things:

-posts stuff to show she has friends
-will change a profile picture very quickly so it shows up in people's news feeds again to get more likes.

I DO NOT GET IT.

I love reading people and stuff, but what would drive someone to do this, particiularly someone who isn't materialistic. For some reason, I get the impression she wants to be seen as popular.....she is well-liked and has some very close friends, so I don't get why she needs likes so bad.