The problem with using the older smallpox vaccine is that it is not a very safe vaccine.
It can pass on to others (be contagious) so you can't get it if you OR anyone you live with has eczema, is pregnant, or is immunocompromised.
You can't get it if you are breastfeeding, have a heart condition, take topical ocular steroids. It's not approved for anyone under 18.
It has hideous side effects, which can include things like fever, malaise, headaches, that start a week after vaccination and can last for weeks. Everyone who gets it has significant soreness at the vaccination site and ends up with a scar.
And it kills 1 to 2 people per million people vaccinated.
Because of this, mass vaccination with the older smallpox vaccine is something we would rather avoid. It's less dangerous than getting monkeypox based on data from Africa, but non-immunocompromised people don't typically die from monkeypox in areas with good healthcare infrastructure.
A more modern vaccine, JYNNEOS, is approved for both smallpox and monkeypox. However, that's not what we have stockpiled. We need to get production up first.
In the interim, "ring vaccination" is a good solution, as is vaccinating healthcare workers.
The big worry is monkeypox getting into the wild rodent population. It's not sustainable in humans (and I suspect the root cause of this outbreak is people who didn't party and travel for two years because of COVID making up for lost time...i.e., it's behavioral, people who's idea of a good time is to make out with others at raves are doing it more and taking fewer precautions because they've had to be so careful). But if it gets into the wild rodent population in Europe or the U.S., we're stuck with it.
Vaccination against monkeypox is not quite the no brainer it is against COVID. If you don't engage in activities that result in a lot of skin to skin contact with strangers, or live with somebody who does, then you probably don't need to be vaccinated against it.
(Note, I don't just mean sex here, I mean if you insist on hugging everyone you meet you might want to consider it ;)).