Originally posted by Wheatfield It's because if the lens isn't perfectly sharp corner to corner wide open or displays any optical defects at all, it will be labeled as junk by people who take pictures designed to make the equipment fail and look at everything at 400%.
We have all been victimized by the zombies who sit in front of computer screens and bray like jackasses every time they are victorious and find one pixel out of 35 million out of place due to some random optical defect.
It costs a lot more to build a perfect lens than a merely very good one, put the manufacturers are forced into a situation where anything less than perfection just isn't good enough.
I think the perpetrators of this are the review sites that make money off of both nitpicking fine details and causing drama (which leads to more viewership). This has grown a larger, overt mentality in the photographer 'world' that it is normal to approach photography in such a manner which then demands review sites (and manufacturers) keep pace.
Yes, if I own a 36 MP camera I'd ideally want 36 MP of detail. But I don't honestly expect it.
But also I think another aspect is in Manufacturers upping their quality based on competition.. when there are five fast 50mm lenses available or a mount how else are you going to stand out? One way is with optically 'better' lens formulas -- more resolution, less CA, edges at/near as sharp as center, faster aperture.. and the side effects are larger, heavier, and more expensive lenses.