This is because of money, not because of fundamental scientific issues.
This time, there was a financial backer (the government) that was willing to fund development of a whole bunch of vaccine candidates, without any preconditions. That's never happened before.
Normally, if you want to develop a vaccine, you have to go to investors, and convince them that your vaccine has a high probability of succeeding, not only technologically but financially. If you're lucky, you find someone to fund phase-1 trials. After those trials are done, you analyze the results, and then go try to convince investors to fund phase-2 trials. You have to finish those trials, analyze the results, and then go try to convince investors to fund phase-3 trials, which are extremely expensive.
If there's someone who guarantees funding for all three phases up-front, you can go a lot faster, without sacrificing scientific integrity at all. You can begin recruiting people for the phase-3 trials before phase-1 trials even begin. You can immediately begin the next phase of the trials once you know the vaccine passes the requisite safety threshold, even if the previous trials are still returning data.
Normally, these things are done strictly in order in order to minimize financial risk. If there is no financial risk, you can do a lot of things in parallel.
> And now it is acknowledged to not protect you or prevent the spread of COVID.
The vaccines reduce your risk of serious disease or death by orders of magnitude. That's extremely strong protection. They reduce your chance of infection and transmission by a bit (more in the first few months after vaccination), but not as much as they protect your health.
> How can you claim any social good here? it has bad side effects and does not work.
The vaccines have likely saved more than a million lives in the US. The worst side effects are extremely rare, and are caused at a higher rate by the virus itself.