There are lots of papers out there that explain why the vaccine was given priory and why funding and expertise were granted to it so quickly. The starting point wasn't zero. The vaccines are based on other research already started.
The main reason other vaccines take longer are done to things such as funding rather than then actually not being able to do it.
Some countries already have vaccine requirements, such as for yellow fever.
Even if it is a requirement for ravel then it's still a choice. For most people travel abroad is a choice. Don't want the vaccine, then done travel to the lances that require it.
Going to a festival or concert is a choice, pretty much a luxury choice for many. It a private event decides it's an entry requirement than it's a choice still.
I would imagine that there would be medical exemptions for all of these too, to cover those who cannot have vaccines.
And then some may allow you to avoid having the vaccine so long as you have a negative test within days of going and/or arrival or have quarantine restrictions in place for unvaccinated people who aren't medically exempt.
I'm recovering from Covid and on my 5th week of absence from work with it. I'll have a vaccine rather than have this again. I'm clinically vulnerable but under 50, so it may be a little while but I'll be signing up as soon as I can.