There are likely numerous reasons, but the flu vaccine update was generally around 40% for adults in the US[0]. COVID is something like 70% and the OP is saying if we got even higher it might've worked. (I suspect the bigger issue was getting it distributed globally.)
> experts were saying this was the likely outcome from the begining
Well only those other experts... the "kooks" and "right wing" ones who "care more about the economy than lives". The ones that got their reputations destroyed.
The mainstream "experts" who are the ones we are only supposed to ever listen to have never really made any of this clear. If they did, we wouldn't even be having this discussion.
If they cared about the economy, they'd be screaming at everyone to get vaccinated so that life could go back to business as usual. The economic cost of millions of people requiring life-saving, high-intervention healthcare is crippling.
They don't actually care about the economy, though. They care about two things - fighting a culture war, and bending over backwards for businesses, at the expense of literally anything else. It doesn't matter that millions of people are racking up billions in preventable medical bills, so long as the Mar-o-Lago can stay open as if nothing happened.
They aren't making a 'trade-off' between the economy and human life. They are utterly failing at protecting both. If you want to see a trade-off between the economy and human life, look at how China handled the pandemic. Harsh lockdowns, vaccine mandates, and as a result[1] - strong economic growth through the pandemic.
[1] Also only 4,000 dead, as opposed to 900,000, but who's counting?
why hasn't the flu been eradicated then?
>It was only after (in the US) vaccination rates levelled off and Delta came along that I began hearing people talk about COVID as endemic.
that's because most people have no idea what's going on. experts were saying this was the likely outcome from the begining