So answer us a question -- name a single vaccine that is 100% effective and has no vaccinated breakthrough cases in an environment where the virus is highly prevalent.
You should note the vaccines for measles, mumps and many other diseases have a much higher vaccinated breakthrough rate in an environment where the virus is highly prevalent than the Covid vaccines.
Hence the need to additional health measures (restrictions, quarantine, social distancing, contact tracing, etc.) when any of these diseases becomes highly prevalent in a community -- even if a majority of people are vaccinated.
The question isn't "is there a vaccine that has no breakthrough cases" but instead the question is a comparison of vaccines and the % of breakthrough cases. Where would the COVID vaccine rank on that list? And if it ranks near the top (and it does, I'm sure) of % of breakthrough cases - then the next question is "does the vaccine pose a risk to those who take it?" And that also is true - there is a risk. So we then compare the risk of taking the COVID vaccine to the risk of taking other vaccines. And again, if it is at the top, then we have a high risk, low efficacy vaccine that is being pushed for a virus that - for the vast majority who get it - doesn't cause danger.
So that's the problem.