[AnotherGoodName]

But it's specifically 25bits not 24?

As in n+1 == n once you go past 2^24 on a float and here they are at 2^25-1. So it doesn't quite make sense as a reason to me.

There's a post above that browsers divide pixels into 1/64th of a unit which accounts for 6bits which puts this limit at precisely that of a signed 32bit integer. This makes much much more sense than the significand of a float.