I can definitely help with on the inconsistent sizing front. Every garment has a "sample size" that you do all of your design work on. It's the size of your mannequin and the size of your fit model. Once you have the sample size garment figured out, it gets graded up and down for smaller and larger sizes. Sample size will be the brands most popular size - almost always a medium (but I believe Patagonia's fit model is a 6). Non-sample size sizes may go through lighter fit checks or sometimes none at all. By going with a middle size like a medium, the grading has a better chance of being accurate vs, say, fitting on a size 2 and grading that shape up to a 16.
The problem is not every brand has the same most popular size / most popular body shape. Bodies change with age. There are similarities across race with some having curvier or more petite builds on average. The most business in fit forms, Alvanon, did millions of body scans and builds a default fit form for each major country market. So an XS pair of women's pants could range from a 33" hip to a 38" hip, depending on which country they prioritize.
Bigger brands can also get their own custom specs made. If I were a ski brand, I could do a mix of US and EU data, pick an age range, and add other demographic filters that I thought helped zero in on the most typical skier.
That's the reason North American-focused brands like Columbia or Flylow tend to fit differently than ones that are pushing global distribution (like Arcteryx), and that the ones that focus on Europe or Asia fit differently too.
Definitely the right move for the businesses, but a total PITA for customers and way overestimates how well customers know their own measurements.