How many people still use TVs these days? Everyone I know don't even own one anymore, though my friends circle might not be that representative of society as a whole.
I don't see why you make that comparison. Many distros (Ubuntu comes to mind) certainly cater to the same market as Windows and OS X, and do it very well.
I don't think this is the problem at all. Ubuntu, for example, is perfectly usable and a very good alternative to Windows.
The main problem, I'd say, is that there really isn't much of a reason to switch. People who buy a computer don't have any incentive to go through the with hassle.
If computers came with Ubuntu pre-installed I'm sure people would use those without a second thought.
It's not nearly that straight forward. Many "fixes" would create incompatible blockchains between the different versions. In practise you need to get consensus before your fork can even be used.