Ostensibly, because Trump "...didn't want to create a panic..." That "Panic" would have been his if the U.S. did the right thing early on and treated COVID-19 like the pandemic it became...but that would have caused a 'kink' in the economy and hurt his re-election chances...turns out he screwed it all up in the end.
That "Warp Speed" moniker doesn't fit very well with what he actually "Did" and said. Oh, and by the way, it was Dr. Fauci who worked with Moderna to get their vaccine candidate fast-tracked into Phase 1 trials on the very day they completed its design...and two days after getting the COVID-19 genome from China...that's real "Warp Speed" by someone who understood the technology from working with scientists during the decades of mRNA development.