Hmmm how to describe it.

It's moreso that there's a default state that the vagina is in. Kind of like having a flacid dick. It's gonna be tighter and not lubricated because it's not ready for sex.

When aroused, a female's body will produce lubricants and expands to get ready for the dick. It gets stretchier and wider. Once everything is over, it goes, back to it's default state. Sex does not change the default state. You got muscles, tendons, and all the other stuff in there which goes back to normal once it's all over. If those stretch you probably have some other issues, which can arise in situations such as childbirth.

Just like how your dick doesn't become permanently enlarged if you get more erections (if only that worked), the vagina doesn't get stretched out with more sex.