The part you are missing is that, like the flu, a SARS virus evolves . That's why people might think they only need four or five flu shots a year and then be good forever like a Measles shot.
Not a virologist so I trust the experts to not screw it up. Are there risks? Sure. There are risks crossing an active street so consider the odds. A healthy adult under 40 was at less than a 2% risk of dying from COVID. The problem, as you've already discussed, was that it rose towards 25% for those over 65. Killing off 25% of a retirement home is bad for business and the insurance companies. Unless there's more money to be made killing of the weakest, then all bets are off. LOL