Why do I even try when they’re obviously not interested?

There's this guy that used to work for the same company as I did. I kinda liked him and I'd seen him on a dating app, but didn't try to talk to him then since I thought it would be awkward. Fast forward 4 years. I'm single again, we no longer work in the same place and I see him on the app again. After debating over it with myself I decided to send him a message. Surely enough he was online later that day, but didn't reply. Now I feel foolish. I should have known there was no point.