They do, though. In fact that's the entirely novel value that this study brings. It's in the title: "histopathological characterization of myocarditis after anti-SARS-CoV-2-vaccination." That's a lot of words that means "we can now tell you exactly what microscopic tissue looks like following lethal jab-associated myocarditis.”
And the scientists discuss how it happens. For your benefit, I'll describe it here.
These mRNA-vaccinated patients suffered from heart damage because their hearts were attacked by their own immune cells. The mRNA is injected into your muscle cells, turning the cell into a factory producing COVID-19 spike proteins. As a result of the mRNA immunization, your body generates an immune response against COVID-19 spike proteins. Since your own muscle cells were used to make the COVID-19 spike proteins and may have them on the cell surface, your newly-weaponized immune cells targeting the spike protein may start attacking your own healthy muscle cells. This autoimmune attack on their own heart cells then leads to their damaged hearts beating so many times per second that, once the tachycardia unexpectedly started, they died in minutes.
This new German study shows photographic evidence that this happens and has killed people