The vaccines don't reliably prevent spread. That is hardly an extraordinary claim, it's an established scientific fact. Fortunately the vaccines are still very effective at preventing deaths.
Are you looking for 100% effectiveness? That's not how anything in the world works. If I can reduce the probability of spreading infection, that is a clear benefit to society. If enough people reduce the probability of spread enough, we can reach a point where for all practical purposes, the virus is gone.
No one is realistically looking for 100% effectiveness. However the vaccines don't reduce spread enough to eliminate the virus. Eventually we'll all be exposed. The main benefit of the vaccines is preventing deaths.