Because once you learn it, notation gets out of the way rather than in the way. I can't imagine doing physics and having to write out words rather than symbols

Because once you learn it, notation gets out of the way rather than in the way. I can't imagine doing physics and having to write out words rather than symbols to express rates of change. It makes sense that specific knowledge uses specific language to be more easily used and manipulated. Imagine writing (or even proving) Euler's equation without using i or pi or e. Imagine what mess math would be if we never used Greek symbols. Sure, it would be easier for middle schoolers. But if you're arguing that we should make it easier for them since they're not gonna need ease of manipulation for math that they're not gonna use... Then just do the teach it to them. Maybe middle schoolers don't need < as a concept any more than they need it as a symbol. But if you're going to solve equations and inequalities, then yeah, you need = and <. Everything else would be needlessly verbose and get in the way of actually manipulating concepts you know.