Redis is a popular program, it makes sense to spend the time to port it. But what your missing is the long tail, thousands of little programs scattered around - or edge cases in bigger ones.

Working on a non-x86 platform makes you a second class citizen, you will experience issues that others have already ironed out on x86. Software has a long tail of niche code not actively maintained but still heavily used. It doesn't make sense to switch to ARM there.