There's a whole lot of nuance that should probably be thrown in to the smallpox history here, esp. regarding the alleged fatality rate, though it wouldn't really alter the core point you are making.

But in particular, the repeated statements that the vaccine should be "credited" with eradication are not supported. Per Henderson, who ran the eradication campaign, the vaccine was at best a part of the larger project which included track and trace, which was feasible only because smallpox is not transmissible in the preclinical stage - https://apps.who.int/iris/bitstream/handle/10665/49813/WHF_1987_8%283%29_p283-292.pdf

"It became apparent that in all endemic countries there was a need for a specially dedicated and trained professional staff at all levels to decide and coordinate the strategy and tactics of the smallpox eradication programme and to modify its methodology according to local needs, to develop reporting and surveillance systems, to undertake case-detection and containment measures, and to train local health staff in vaccination procedures and the proper preservation of vaccine."

So it wasn't like they just vaxxed everyone and called it a day. Indian states had extensively promoted vaccination for over a century with no apparent reduction in transmission until the eradication campaign added isolation/tracing (https://journals.lww.com/ijmr/Fulltext/2014/39040/A_brief_history_of_vaccines___vaccination_in_India.4.aspx). In the global north, early-20th Century reductions in mandates were not followed by outbreaks. So it seems like a leap to even assume, without better proof, that the vaccine was even instrumental. The history of the virus is very puzzling in a lot of ways, besides.