The difference is we know how to make the bridge, and knew where to place it. A lot of the effort in a new bridge is work that didn't have to be done for that bridge because it was already done. No need to figure out what to do with traffic (which means no phases that must complete first). No need to dig new footings, just use the old ones. No need to do a new design - the old one was good enough.
The bridge collapsed because of a fire and there seems to be no reason to redesign bridges to resist a fire like that so a lot of effort was saved. If we decided fires were too common we wouldn't be able to replace bridges as quickly because we need to do engineering work first on a new one.
We know a lot about making viral vaccines too so we have a lot of companies so a couple different methods get used and at least a few of them pan out. It's like if we could have 20 companies try to build the same bridge without interfering with each other and whichever worked became real.
The bridge collapsed because of a fire and there seems to be no reason to redesign bridges to resist a fire like that so a lot of effort was saved. If we decided fires were too common we wouldn't be able to replace bridges as quickly because we need to do engineering work first on a new one.