It does make a big difference. I suspect the creators of ergonomic mice never considered it. Ergonomic mice is a niche market, it’s not like the guys making them have big teams of researchers. I wonder what the backgrounds of ergonomic mice creators even are. They probably have some mechanical engineers on the team, and hopefully some product designers. Few people involved in designing or building peripherals seem to have any particular background in hand anatomy or human factors research though. When occasionally there are some real experts involved in making a product (e.g. the MS ergonomic keyboards) there are usually so many other design constraints (low cost, similarity to existing products) that they don’t have anything even close to carte blanche to design a product starting from human anatomy and working up.
Every commercially available mouse I’ve ever tried used little microswitches. Similarly, every commercial calculator, phone keypad, microwave, coffee machine, video game controller, etc. uses some crappy mushy low-travel switches, or the occasional nice one uses microswitches. Just be glad they aren’t moving to capacitive “buttons” like I recently had to use in a rental car: they looked like buttons, but didn’t depress at all, instead getting triggered via capacitive sensors when touched – except 3/4 of my touches did absolutely nothing. Unbelievably frustrating.
Would it be better if vendors did extensive research on switches to find the most effective one for their application, and then used those for their products (at least in some deluxe alternative version)? Of course. Is anyone going to do that? No. (Which is kind of sad considering how much e.g. video game controllers or “modern” graphing calculators sell for.)