Visa exempt means the applicant doesn't need a special travel visa to come to Canada. They can just show up in Canada, and get a 6-month visitor status on the spot. Usually it's a very easy process for a visa-exempt applicant to extend their visitor status.
Visa-exempt visa offices are also usually very quick (Ottawa, London, Australia etc). So in many cases outland applicants get their full PR, quicker than it takes to get just stage 1 of inland.
i.e. For US applicants outland PR apps are processed through CPP-Ottawa. Current times people are seeing today is around 8-10 months, and usually US residents can visit Canada very easily. So it really makes zero sense for any US applicants to apply inland these days, unless they think they will have some admissibility issues visiting Canada during the process.