[woah]

Why do forms require signatures if it's easy to forge (especially if you are submitting it electronically), and evidence of the agreement is gathered from other sources if it comes up in court?

Because it boils down what could have started as a nebulous mix of halfway-unethical actions into a single fraudulent act that can be pointed to and punished later, and will provide a lot of people with the impetus to back out of the fraud once they see themselves about to commit an unambiguously illegal act.