Being teetotal excludes you from a lot of social events, and even somewhat unrelated events. We have hiking/fitness groups that typically end the training session with a round at the pub. Many workplaces go to the pub together after work.
Not engaging with this can set you back socially and professionally, because drinking is hugely ingrained in the British population. Most people drink multiple times per week. The people I work with genuinely struggle with "Dry January" and other such abstention events.
Going along to these events and not drinking gets you interrogated, and it becomes a thing to try to get you to drink / get drunk. It's probably an inferiority complex thing on the side of the people drinking because seeing somebody not drinking makes them feel bad about it (even though they needn't feel that way).
For every one person like you that doesn't care, there's many who really want to investigate it and get to the bottom of it. Telling these people you just don't like drinking isn't the solution they're looking for out of their investigation.
My 2 pennies as a lifelong teetotal.
I can assure you someone will ask if you're okay, urge you to drink "at least one", or "just a glass of Champaign, it's a special one".
I always read this on HN but I've never cared, or met any adult that seemed to care, when only a few of us drink beer in a group. Is this a US/Anglosphere thing maybe?