Not really reinventing the wheel, just using up to date technology which happens to be somewhat incompatible with the old one. I say somewhat because it's only on a phone that it becomes more trouble than it's worth. On a desktop it doesn't really matter as you can run anything with minimal effort and there is enough horsepower for any compatibility layers. The only exception is the one railroadmaster pointed at, which is Canonical (the developer of Ubuntu) reimagining perfectly round wheels as cubes all the time. If they invested their money in helping others fix the real problems with new software, which is sometimes incompatible because it's impossible not to be, I think we would be several years ahead of where we are now. They have lots of money, but choose to spend it on making knockoffs of popular software, with "© Canonical" in the credits. I wouldn't be surprised if one day they forked the Linux kernel so they could call it the Canonikernel.

The biggest difference between distributions is the software they include by default. New microdistributions pop up all the time because there are always some lunatics who think they need to "provide a choice for the people" by making a distribution that does exactly one thing different to the parent distribution just because after an argument on a mailing list the parent distribution (or developers of a particular piece of software) ended up not changing a certain feature, and so the people will be freed from the oppressive chains of the parent distribution. In reality, they waste a whole lot of time trying to keep up with the upstream development, all the while making sure their particular preferred feature still works and evangelising on mailing lists and forums about their heroic efforts to save x from certain doom, only eventually noticing no one really cares about those efforts. But then two more heroes of the people will have risen up to repeat the cycle.

This is not to say people can't disagree, but it would help a lot if those disagreements didn't have a guaranteed end result of split efforts.