Would take 2-3 engineers how long -- I can't really see it being more than a couple of week project. But, why would they? Seems they'd only do it if there's a ROI, is there?

If Google gives you what you want straight away then you leave; sure, you come back, but they want to be bad enough to keep you on there and good enough to be better than other searches. Their reach and resources cures the latter.

Google adding dedicated optimizations for popular sites seems like a bad trend.

They do it all the time.