the issue isn't that people won't believe it or that blockchain can't preserve secrecy of ballots (it can). it is, in part, that crypto eventually has to meet the real world, but mainly that crypto is hard and governments might not be up to the task. for example, last year the IACR (which had been doing online voting via crypto for more than a decade, and still is) had to void their elections because one of the trustees lost their private key and the results were impossible to decrypt. while it was ultimately fine because the IACR isn't really a high-stakes operation, how would you feel if your government just said "sorry folks, there's been some technical issues and elections will have to be redone"? would you believe them or suspect they're up to no good? what if this happens in a very contended and heated election?