It’s the same as with Linux, GIMP, LibreOffice or OnlyOffice. Some people are so used to their routines that they expect everything to work the same and get easily pissed when not.
The main reason is that ux design is difficult, complex but not always rewarding. Few people do it “as hobby”. Companies make money out of UX design. As in the example of Apple, they could find a lot of open source good quality software, but they needed the ui to seel it in macs, iPhones and ipads.
Another example is steam deck. Its OS is just arch linux, with an incredible UI (built by valve), and it is currently more popular than windows handhelds.
Many open source solutions are of greater quality than corresponding proprietary stuff (anyone who has ever worked in a corporate environment also knows why, corporates are elephants trying to create a swiss watch). What open source solutions are missing are companies paying to create user experience.
