Why do African men tell American women that they love them so quickly and don't even k now them?

This is certainly not the first time this has happened to me, but for some odd reason, A lot of African men are attracted to me. I have never spoken with an African man in a sense of dating because quite honestly, I'm not interested in dating anyone that lives in a different country But whenever I join Facebook groups or some dating sites, my inbox usually has a small handful of African men. I am always upfront and tell them that I am not interested in dating overseas. That seems to attract them even more. This past instance I was literally about to close my account on a particular dating site, but I couldn't find the delete account button. I had an email. I shouldn't have opened it; I should have deleted it and walked away, but I'm a nice person and I try to respond to every email that I get. I told him I was deleting my account and he asked if I had an email where we could chat. (WHY OH WHY DID I GIVE HIM MY EMAIL??!! That was a mistake on my end. I told him I was not interested in a relationship. He says can we be friends? Ugh! Why am I so nice? lol. I try very hard not to lead him on. Careful about what I say. Attentive to how much time I give to him. At one period, I stoped my notifications so I wouldn't be tempted to respond, at least not so quickly. Our conversations (if I can even really call them that) are very brief, and not deep. This last message he tells me he loves me. That is not a turn on. It's actually the opposite. This man doesn't even know me. Why are a lot of African men to tell an American woman that he loves her so quickly and doesn't even know her? Besides trying to get a green card, what are some other possible reasons?