Not endorsing, but allowing is aimed at letting people feel like they aren't being handled like children by their employer, and, as alcohol is a very common component of social interaction in western culture, is meant to make it easier for workers to socialize and make friends with their colleagues. I'd imagine the reason for wanting that is something like that employees who are more connected with each other are more likely:
a) to want to stay at the company with their friends, less turnover
b) to be happier at work which is good for performance, recruiting, and makes them less likely to feel the need to rush out of the office whenever they can.
c) to efficiently organize themselves and find the right people to get things done if they know each other well
d) to be transparent to each other and reduce friction in communications
You might not ever have some beer or wine when you socialize with people, but for a huge number of people that's viewed as an integral part of socializing.
a) to want to stay at the company with their friends, less turnover
b) to be happier at work which is good for performance, recruiting, and makes them less likely to feel the need to rush out of the office whenever they can.
c) to efficiently organize themselves and find the right people to get things done if they know each other well
d) to be transparent to each other and reduce friction in communications
You might not ever have some beer or wine when you socialize with people, but for a huge number of people that's viewed as an integral part of socializing.