What you do now is let it go. Don't hold onto the resentment because at the end of the day, they didn't care enough to spend time with you. Some may have had good reasons. Others may not have.
It's their issue. The best you can do is to spend more time with the folks that did come. Ask the 5 friends (or one or two) if they want to do something with you next week. Pick an activity. Doesn't matter what.
Fruit bats eat corn...
Learn something new every day
Edit: a letter.
A lot of commenters here are saying a lot of similar things. I'll offer my own insights.
As people get older, you have less time. Between maintaining a relationship, doing chores, work, etc, there are so many hours to do things.
As a result, a lot of FOMO happens. It's not about you. It's them. They may plan to come to your birthday. They may even want to. But suddenly, something else comes along that they want to do instead.
I don't plan big events anymore. I'm in my 40s and just dgaf whether people make time for me or not. I'll ask one or two friends if they'd like to go out to dinner for my birthday or some event.
I really don't want the definition of the word "hack" to get expanded to "someone registered a domain name and set up a website that closely resembles the official website".
I accepted "hack" to be a black hat definition, which used to be "crack".
I thought this was my imagination. I had to treat a really bad case of athlete's foot with prescription grade antifungal medication because the over the counter stuff wasn't working.
Two months of twice a day treatment. And if I forgot a dose, it became much worse than I expected.
Pied Pipper at it again.
"A lie will fly around the whole world while the truth is getting its boots on."
--Mark Twain
"If our votes had any real power, it would be illegal!"
--Britta Perry
But seriously...go vote.
The West Wing Weekly touched on this in one of their episodes. Basically they are turning more to focus groups where participants are paid a small amount.
At this point, polling should assume a conservative bias.
Because, even for Nazis, it's the inside that counts.
Nazism will even cover up for the sin of you not being white.
Very very eye opening. Thank you
If Jesus was alive today, he'd be crucified again by the Religious Right.