This is hardly true. Mathematical notation changes all the time-in fact, inconsistency is a significant problem, because Mathematicians love to experiment with notation, definitions, etc.
Seriously, just look at a Mathematical logic book from 50 years ago vs. one today. You won't even recognize half the words, let alone the symbols.
The notation of mathematics is centuries old. It's very hard to take notation away from the set that must be learned, but easy to invent more.
Eventually old constructs can fall out of favor, but that is a long and slow process.