Valenwood is where the original Thalmor Headquarters use to be. Considering it all started there before Tiber crushed them, I see no reason why majority of the Bosmers would not side with the Aldmeri Dominion.
Also Khajits didn't get tricked.
Because most modern Bosmer would not have grown up under a Thalmor government, but instead an Imperial government (or a government that the Empire provided for, which again, wasn't Thalmor) and as such most would not be very privy to being lorded over by a faction that generally isn't primarily Bosmer anyway. The Valenwood coup was staged by a few Thalmor-sympathetic Bosmer factions. Everyone else who didn't decide to support the Thalmor from then on went on to be absolutely screwed.
Need I mention the purges that have been going on for just under 200 years in Valenwood now?
And the Khajiits were tricked. The moons did disappear, but the Khajiit were made to believe that their return was due to the Dominion, which of course was absolute crap.