You can point to individual reasons. Prices, smoking ban, supermarkets practically giving it away, everyone's skint. All valid reasons. But the fact is that the total number of pubs in the country has been on a steady decline for at least 50 years. Probably more. And most of the reasons above weren't really a factor for the majority of those years.
Bottom line is that people's habits change over time, due to a whole wide range of issues.
There will always be a demand for pubs in city centres and larger town centres. You go to town on a Saturday afternoon, and your problem can be finding a pub that you can get served in a reasonable time and find a seat, rather than a lack of them. With plenty of people of all ages.
Go to a 'traditional' out of town pub and the average age is gradually getting higher and higher. There's more people in there at 11 am than 11 pm. Those type of pubs will continue to close as the regulars die off and aren't replaced.
I predict in a couple of decades time, if not sooner, pubs will be a bit like restaurants. You still won't be able to walk a few yards in town without stumbling across one. And more affluent areas like Didsbury and Chorlton will still have a good selection. But they'll be virtually non existent in what you might call 'working class' areas. Look at Moss Side and Hulme. They're almost there already. And Wythenshawe isn't far behind.