One purpose of the site is to help bring people together who have complementary language goals so they can help each other. To that extent, the "language partners" portion of the site is in fact intended to allow "strangers" to contact each other. If you don't want people to contact you, you can go to "settings" and "privacy" and make selections so that no one can send you follower requests and only people whom you are following can send you messages.

If you mean strangers when you say "strange people" then yes.  All requests from strangers are to make language friends with someone.  They do it because they want to learn the language that you are familiar with in exchange for teaching you their language.  And because of cultural & language differences, these requests can come across as strange or awkward.

It might be they want to learn your language. It also might be a cultural thing. Or it could be they think it is cool to have a foriegn friend. When I taught in China everyone wanted to be my friend because I was the cool foreigner.

You are in the language site and people want to learn your language. Where is the problem?!

they do it because they want to know people from somewhere else to be a friend with someone they did never met and perhapse talk to someone  who didn't already judge them .

some people do it as an adventure , and some times it gives you a good experience and maybe some lesson