There is nothing wrong doing some of the non-medical things letting setting up for manufacture or distribution in parallel. However, some things about the length of normal trials for phase 3 can't be compressed. If it normally takes 6-9-12 months to test a large enough volunteer population for LONG TERM side effects, not sure how you can safely shorten that. No one has yet come up with a treatment or cure for covid, but somehow those working to develop a vaccine has all stumbled on the right formula on their first try?
It's much easier to make a vaccine than find an effective treatment. The immune system response is fairly well understood and works the same in most people, so there isn't as much trial and error involved.
Most of the vaccines in trial SOMEHOW target the virus' spike proteins. This is a vulnerable characteristic of this virus, which ends up being fairly easy to teach the body how to attack.
Plus, the groundwork for the mechanism of the vaccine was laid 10 years ago when they were working on developing a vaccine for SARS, another coronavirus. So, all they had to do was refine it to target this virus specifically. The virus genome was sequenced and shared by scientists very early in the pandemic, so they had everything they needed to develop a vaccine.