When a voter makes a mark, the chain of trust between their intent and their voting record is complete. They know that record is an accurate expression of their intent.
When they provide input to a computer, their direct expression of intent is not stored, instead the record consists of whatever the computer understand their intent to be.
If it records anything at all! Their record ends up being a smudge on some input device.
There is no enduring record. In other systems, redundancy and public records help fill this gap.
Banking provides receipts and or redundant transaction records.
If the voting record is public, this would suffice, but a public record comes with it's own issues.
Without this, there really isn't a way for the voter to understand whether the record of their voter intent is both accurate and enduring.