GPG has a chicken and egg problem. I have mine publicized on Ubuntu’s key server, which is likely one of the bigger ones (but iirc it is of little relevance as it syncs with other keyservers). Out of the emails I am sent only one of my contacts bothers with encryption. Which is sad, but what can you do? The web mail interfaces rarely if ever support GPG, and even if they do sharing your key with them defeats the purpose.