They're different titles though. Grandmaster (GM) != Woman Grandmaster (WGM). Judit Polgár, for example, peaked at an Elo of over 2,700, so she easily qualified for Grandmaster (requirement of 2,500).

Similarly, a Brigadier General is not the same rank as a General, despite some commonality in word choice between the two ranks.

Well OK, but it doesn’t explain why there’s a WGM. There isn’t a “woman sergeant” position, and we’d definitely take offense at a company defining separate “senior engineer” and “woman senior engineer” positions.. so why accept the condescension of WGM?

Not all female players do:

"These titles are sometimes criticized and some female players elect not to take them, preferring to compete for open titles. For example, Grandmaster Judit Polgár, in keeping with her policy of playing only open competitions, never took a women's title."

https://en.wikipedia.org/wiki/FIDE_titles#Women's_titles

If the titles required the same Elo to achieve then there wouldn't be a point to have separate titles. The female-only titles are useful to encourage women to compete imo.