You're welcome as a fan to think that's one of the reasons but the main reason is he's simply just not good enough except on clay. Btw, I'll cut you some slack regarding his injury at the AO 2014 as this was obvious in terms of his movement later on in the match (though he was getting his ass soundly kicked before he got injured and we'll never know how the match would've entailed) and RG 2016, though this was impossible for anyone to see as he absolutely mangled his first 2 opponents and then stopped playing. Strange. VERY strange. 2009 and 2012 most people saw zero sign of injury whatsoever and they remain dubious to this very day and really only hardcore Nadal fans believe he was injured since there were no visible signs of any impairment.
He also played quite a few more years than those 4 and never defended a single tournament that wasn't on clay but nice try all the same.