They are. But you’ve never heard of most of them, and OSes aren’t popular because of their merits.
No real need or funding. Designing a new kernal is not an easy task and no matter what youre gonna run into hardware compatibility issues. Why waste time on that when there are plenty of open source gnu/linux based distrobutions that are both free and compatable.
Im sure there are people out there designing a completely new alternative kernal as a hobby but it would inredibly unlikely for it to reach the popularity of gnu/linux, windows, or mac
They likely were making the operating systems while balancing their job to cover expenses like rent and food.
There are. They just don’t have a lot of popularity. Take a look at RedoxOS for example.