If Google has been merging ChromeOS and Android for 2 years, they must have reasons... since the tech is all crap, we're talking about business/logistic strategy. I can imagine a few:
1. Chrome OS was a hedge on "HTML5 webapps are the future". Seemed like a good bet in 2008-09 but it hasn't panned out so well.
2. Consolidation. Having two in-house Linux flavors leads to confusion, bugs, fiefdoms, and... expense.
3. ChromeOS (along with CoreOS) is based on Gentoo which is maintained by a bunch of yahoos who probably don't have Google's corporate interests at heart. Systemd could be a sticking point: AFAIK Google went all-in on systemd, but in Gentoo it's optional, non-default, unloved, not exactly "fully supported"... which means Google's probably got a ton of package mods that get whacked by every other upstream update. What a pain in the ass. <Points and yells "systemd losers... HA-hah!">