It’s true that many people go to seminary for shidduchim. That’s why BJJ has so many girls who don’t belong there:) Well, that and name-dropping.
That being said, not everyone takes shidduchim into account when choosing a seminary. People do try to find a place where they will grow spiritually, emotionally, and intellectually (in that order-or at least that’s the point of sem, IMO), gain more independence, find new friends, and generally change for the better.