It's just habit.
I'm a plumber and my tools are of 4 different battery platforms, doesn't bother me.
Granted, they are kind of "grouped by task" so it's highly unlikely to use all platforms at the same day...
I own the Hilti TE6-A22 and i have also worked with the Milwaukee CHPX, Dewalt DCH273 and Dewalt DCH283.
Overall, i think the Hilti is the sweet spot for doing everything.
The Milwaukee CHPX and Dewalt DCH283 hit harder, but they actually don't drill faster (or not faster enough so i could...