COVID-19 Outbreak Information Updates (Reboot) [over 150.000,000 US cases (est.), 6,422,520 US hospitilizations, 1,148,691 US deaths.]

That's an excellent point. I would love (and I know this
I don't agree with them. Vaccination does help prevent transmission, since it reduces the risk of being infected in the first place, and if you're not infected, you're not infectious. Additionally, Covid-19 itself has a substantially higher risk of myocarditis, and that also tends to present itself more seriously than the rarer vaccine-associated myocarditis.

So, assuming the risk of exposure to Covid is substantial, then vaccination offers an overall reduction in the risk, and potential severity, of myocarditis. Plus the indications are that it reduces the risk, and severity, of long Covid, etc.
Then there is the viral load aspect.

Viral load has a huge impact on transmission, and vaccinated people who get the virus will have a much lower viral load.

So while the vaccine doesn't prevent you from transmitting the virus, it absolutely makes you a less effective transmitter when infected, by the same mechanisms that make your severity of disease symptoms much lower.