Why is it so awkward to go out places as a single person?

Why is it awkward to go places alone for fun as a single person? I (29M) have been single pretty much all of my adult life. Usually it’s not a big deal, but as I get older more and more of my friend group has dwindled away. They get married and start new lives and I rarely see them. I wish them well, but I want to continue my own life, so I go places solo more often. However, when you go to a concert, convention, church, or other event solo you’re often made to feel awkward. People look at and interact with you differently. It’s like subconscious coldness toward you.

For example I went to a convention today solo that I had always gone with friends to previously. It had always been a good time and I usually met lots of friendly people. But today the vendors were rude and obviously just wanted to grab my money. The other attendees were pushy and hardly anyone acknowledged my existence.

Another example, I go to church solo most Sundays. I almost always arrive early and pick an inside end seat so that I’m not blocking a row. Then I get rude looks from people who show up late and almost literally try to push me out of my seat. One time someone nearly sat on me without acknowledging me or even asking politely to move. I volunteer at church and have been involved there a number of years, but most people still ignore me. Then for a couple of weeks I brought a friend to church and it was totally different. People talked to me who never did before and it as if they laid out the red carpet.

Am I alone in this experience or have any other single people experienced this?