It is unfortunately becoming more and more common. Similar thing is when a site will only work with certain Internet browsers. I use Firefox all the time, but there are certain sites that won't work in it (even though it meets all W3C standards etc), so I have to use Edge for those, my daughters school monitoring site being one of them.
Same thing can happen with Safari on Apple kit -if you try to use another browser on Apple kit there aren't many, and they all use Safari's engine anyway as Apple won't let any others on, so if ithe site doesn't work in Safari you need to get something that isn't Apple....
Accessibility compliance is also pretty dreadful, the trend for "flat design" in various shades of grey has made things even worse. You do wonder what sort of testing these designers actually do!