Docusign and other services like it do more than send out forms to collect signatures. There often are other fields / data collected, alternative forms of documents presented depending on target party's profile, etc. If you take the sign/scan/send form, the receiving company still needs to do all the work to put that form in the right place and perhaps extract further data for further steps in some data pipeline. Docusign et al will presumably integrate straight into your document flow, much simpler in the long run with fewer people.

Just to put one alternative company into the fray, there's Docsmore (https://client.docsmore.com/features.html), a local startup (North Carolina) that offers document management / signing / document flow as a service. I'd imagine it would be hard to go up against a giant like Docusign unless there are compelling additional features.

The Docsmore founders seem to have more recently used the service as a jumping-off point for a separate insurance claims-processing automation company, Benekiva (https://www.benekiva.com/) (Iowa/North Carolina). That seems even more lucrative than straightforward document signing/data-collection.

EDIT: I have no relation to the company, I've met some of the founders before

Who has scanners (and printers) these days? And going to Fedex to print/scan is a cost too.