Electronic ballots are vastly easier to hack than paper ones, and hacking of them is much harder to detect or verify, particularly by non-electronics/computer experts, so the way you detect or catch electronic hacking is generally much more easy to corrupt/subvert than how you verify paper ballots.
Basically, if your ballots are all electronic, you’d better really really trust everyone involved in implementing and verifying the voting. If there are groups with profit and power on their minds interested in the outcomes, and they have billions of dollars they’d be happy to invest in getting a certain outcome, it’s much more likely they can make that happen to an electronic system than to a paper system where there are many ordinary people involved in the process.