Those differences actually make sense to me. If you try to sell pants with the same length inseam in Honduras and the Netherlands, you’ll either prop up the local tailoring industry or fail. Those at least have an inseam measurement, but a medium shirt is going to have to be made for different proportions as well.
I think men’s and women’s sizes could be adapted to be more focused on body shape and less on gender, but I get where they’re coming from. Women are on average smaller than men, so a women’s medium will similarly be smaller than a men’s medium.