Probably because you were the easy one? That was what it was for me, didn’t realize until my mid 20s (covid really wrecked havoc with my studying in college because I couldn’t go to a physically separate space that I had designated as a place I couldn’t goof off).
Samsies, my sister had other issues and was for sure the one who needed more effort from my parents. Meanwhile, I got A’s without much effort in HS and for the most part in college (until Masters, which of course landed me with a bit of a breakdown and being depressed for a long while). I’m not formally diagnosed, but that’s mostly because I feel it’s largely a waste of money for my case (I checked into it a while back when I had terrible insurance, and it was gonna cost me something like $1200).