COVID can also cause this inflammation.
Can and does. Big 10 college athletes are regularly screened for heart issues and they found 2.3% of their athletes with COVID-19 had myocarditis. (https://jamanetwork.com/journals/jamacardiology/fullarticle/2780548)
So out of 1 million, that would be 23,000 cases of myocarditis caused by COVID-19 versus 16 cases caused by an mRNA COVID-19 vaccine (https://www.aappublications.org/news/2021/06/10/covid-vaccine-myocarditis-rates-061021)
16 vs 23,000? Yeah, I know which one I’d go with...