Because the "no hospitalisations or deaths" claim from the first Oxford paper was comparing n=2 to n=0 and thus was miles from significance. If the new paper has updated data on this happy to be corrected.
It is a constant in any vaccine, including the "lowest" performers from Sinovac and Sinopharm. At this point, I'm inclined to believe that any resonably effective vaccine will have this effect.
Tbh, the reductions in hospitalisations has been super high for almost all the vaccines, which is great news.