system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it that scientists were able to completely eradicate smallpox, but they cant do that with other diseases?
gpt
There's several factors: 

Smallpox only had a couple of strains to worry about and the vaccine worked against both.  

The vaccine was cheap and really easy to produce. 

The vaccine itself was infectious, which helped spread immunity.  

Smallpox is such a nasty disease that many countries already had vaccination programmes or even compulsory vaccination, making it easier for so many countries to agree to the massive eradication effort. 

The fact that there aren't really any other diseases which have pushed us to such effort is probably a good thing!