If you've already had COVID, especially recently, that's a pretty damn good reason to not get vaccinated given that your immunity is likely far stronger and more durable than a vaccinated-but-COVID-naïve person. [1]
While getting vaccinated on top might help (there is not definitive data on this yet AFAIK [2]), it is also not 100% risk-free. So why would you do that if you're already more immune and thus less of a risk / less at-risk than the vaccinated population?
For some people it might make sense to still get vaccinated after COVID recovery. But for those who choose not to, it's not at all fair to say they are all "idiots" or that there is "no reason" not to still get the shot. That's not accurate based on what the actual science tells us at this time.
[1]: https://www.medrxiv.org/content/10.1101/2021.08.24.21262415v...
SARS-CoV-2-naïve vaccinees had a 13.06-fold (95% CI, 8.08 to 21.11) increased risk for breakthrough infection with the Delta variant compared to those previously infected, when the first event (infection or vaccination) occurred during January and February of 2021. The increased risk was significant (P<0.001) for symptomatic disease as well. When allowing the infection to occur at any time before vaccination (from March 2020 to February 2021), evidence of waning natural immunity was demonstrated, though SARS-CoV-2 naïve vaccinees had a 5.96-fold (95% CI, 4.85 to 7.33) increased risk for breakthrough infection and a 7.13-fold (95% CI, 5.51 to 9.21) increased risk for symptomatic disease. SARS-CoV-2-naïve vaccinees were also at a greater risk for COVID-19-related-hospitalizations compared to those that were previously infected.
[2]: https://www.usnews.com/news/national-news/why-covid-19-vacci...