Why not? Funding vaccine research seems a worthy endeavor even if some of the research doesn’t pan out. The end result doesn’t need to be an immediately usable vaccine in order for the time & money spent to be worthwhile. Even a completely failed vaccine project could yield a piece of information that helps ensure the next project doesn’t fail.
Because money is finite? Not every research grant gets funded. So let's start with the most promising ones?
Funding vaccines that are not meeting standards should be dropped so that standards can be met. These companies don't need money for R&D, they have enough and can recoup it if they create a product that the market wants.
Most of the vast amounts of research funding given isn't really research, it is scaling up production - a much harder problem that needs much more money. Since we now know of some issues (that would be very hard to find before a large scale roll out - lets not put undeserved fault on anyone here) the labs can focus on them.