Duos refuse to play with me after getting higher rank than me

Why do people obsess over ranks so much? I've had two cases of duos that I played with for months, suddenly refuse to play with me if they're at a higher rank. The rank difference isn't really that high, like two divisions(ex:diamond 2 and asc 1, plat 3 and d2 after reset), but they still won't play with me and come up with the same excuses when I ask them to. Is the elo really that different? Why are they doing this? Do they think I won't do as good as them? Almost every game that i played with them, I was able to put up solid numbers, matching theirs, and sometimes even match mvping. Sometimes I have one bad game but it wasnt really a problem and they still wanted to duo with me after. Now that they're at a higher rank than me they don't want to play with me at all, and would rather play with higher ranked players. It's really discouraging and just makes me feel bad about my rank in comparison to them.