Or they decided to do the hard thing (refreshing a large portion of their lens lineup) before doing the relatively easy thing (increasing pixel density in a single body). As has been noted numerous times, both the optics and the electronics net the effective system resolution, hence the 5D3 + lenses resolving better on average than the D800 + lenses.
Sure; but didn't Roger Cicala at lensrentals show that while the Canon 24-70 2.8 L II is a higher-resolution lens than the Tamron equivalent, the Tamron on a Nikon D800 outresolves the Canon on a 5DIII?
I don't know, but I don't doubt it. My point was that if and when canon decides to turn out a higher resolution sensor, their lens lineup will be ready.