I read few things here and there and just giving you a brief.
Looking at the current pandemic, the IRCC agent can take the envelop for paper applicants and work on them at their home. For online applicants the issue might be more of a security reason that they can't access certain things on internet ( not sure what jargon to use lol ) and that is why there are limited applications being processed for them. As we move in future, once everything is back to normal Online applicants would get more traction as it's easier to work on them rather than handling all the paperwork .
In short - Paper for now, Online later