People took issue mainly because the App Store is the only way to get apps on iOS devices. And they took even more issue with the often random and vague rejections.
I have mostly found the rejections I encountered from Apple to be good things (I've had about 8 - 10 app rejections over the years). They have always led to me improving the app for the customer (e.g., include battery warnings, make text more visible, ensure app complies with child privacy laws, don't include placeholder artwork, and so on).
The App Store's curation is one of the things that increases its value. Even though developers hate it (and perhaps feel slightly disrespected by it?). I'd argue that its been a good thing.