That’s not an alt account, that’s a smurf, which has been said to you multiple times now, but you don’t seem to be understanding.
And alt accounts are good for practicing heroes that you aren’t good with, without tanking your MMR.
You have MMR in quickplay also, you just can’t see it.
And this also. Most players aren’t trying very hard to win QP games. Or at the least, not as hard as they would be if it was comp.