Imagine if you get home and there waiting for you in the lounge is Marillon Cotillard*, covered in whipped cream. Would you go down the local brothel and pay £50 to shag Ann Widdecombe?
You see, beer is just beer. Yes, you can find some obscure ale from North Yorkshire, but most people go to the pub for social reasons. And they want to sit and talk to their buddies. If some of that involves talking to their buddies in the pissing rain, or interrupting their conversation to go outside occassionally, then that's a worse experience than just drinking at home. Oh, and drinking at home is also cheaper.
Now, there's certain things that break this rule, such as going out to the pub to meet up as a group. At that point, the pub wins. If you want to pick up some skirt, you won't do it staying at home. So, even if you're a smoker you'll go to the pub just to get some, despite the downsides.
*Marillon Cotillard is this blog's current definition of top totty