Why do company culture initiatives feel like marketing exercises?

That's what they are.
They're selling you the idea of loyalty to the company in exchange for cheap food, cheap plastic cups, gimmicks like beer-hour fridays, and forced socialization. It makes you feel guilty if you don't buy into the idea (read: lie) because everyone else seems to.

You know what else does this? Cults.

@Root Another point of such brainwashing initiatives is to find heretics, usually disguised as "being open for constructive criticism". See James Damore what happens next.