I believe joining the EU would boost the economy, increase global influence, improve collaboration and provide stability & freedom. I believe that Brexit hasn't brought any tangible benefit and there is no future prospect of any, that the UK has changed its mind and that this should be recognised.
Why shouldn't it work? The EU is open for new members. As a recent EU member, UK should fulfill all requirements for membership. If the UK gov wants, they can apply for membership and that should be relatively quick
One of the requirements is a unanimous invitation by the countries already in the EU. Countries that remember the circus it was every time anything had to be approved in the council because of the British government. The chances of UK joining while a single country can still veto decisions is about 0.
Why? Because they just left...? No idea if the representatives of all those countrieswould just allow them right back after they talked so much shit about the EU and then proceeded to do so much damage and extra work.