Another reason: there's a reason startup offices are so "fun": they don't want you to leave. Nerf guns and hard liquor make the office seem like a place to hang out at, so working 10,12,14+ hours a day doesn't seem so bad. You're hanging out with your friends, right? Overtime pay? Never heard of it. We get stock options right? No, our founders wouldn't dilute our shares to favor late stage investors, would they?
So maybe that's the problem.
Apple really championed the "beer bust" culture in the early 90's.
I have been in "dry offices" and do find it a morale killer, because there's the sense that the HR department knows better than you.
We have beer in our office, and a bottle or two of hard stuff, but honestly no one ever touches it. We have a hard working and professional culture and know alcohol and coding don't mix. ( Or, as I say, "Don't drink and write drivers." )
Sometimes the inside sales guys knock off at 3pm on a friday and have a can of beer. They start early - calling the east coast - so it's good to see them blowing off a little. More professionally, we tend to troop to the dive bar around the corner, which is honestly more fun than setting up a kegerator.
Having beer and not drinking it is a more solid culture than banning beer from the top.
And it has consequences.
The startup culture is very toxic in terms of use of psychotrops. People takes all kind of drugs (alcohol included) often with a laxist attitude from supervisors and drugs + workload + stress = lot of catastrophs. Ho! And of course, the more crunches the more open bar there are to reward you from keeping on with the good job and release the pressure. EDIT and it happens that drinking overlaps with production duties during crunches, when people are already lacking of rest. Thus, generating of course more production incidents.
Startup are brain crunchers and are free to go on since there is no legal liability for this, and they don't pay the price for the damages since they just fire burnt out employees who have to pay for fixing themselves afterward and tell customers there are no guarantees software works, it is a lose-lose-win situation.