The simplest default position from an immigration point of view is that Citizenship ranks higher than PR which in turn ranks hire than any other non PR status be it employment/non employment. Each country has an approach towards time considered as qualifying for Citizenship. By default PR status as the only considered time for citizenship makes logical sense from a ranking perspective and its also a tool to control the inventory if need be. There is a political angle to this too - PRs and Citizens merit more consideration..in fact Charter rights in Canada have a bias towards them for entry/remaining in Canada. It sucks for those applying under the SCCA but Canada was an exception amongst peer countries in accepting any non PR time capped at 1 year towards the qualifying period. Several countries including the UK in contrast credit different times to different visa status so you need more time as a student (10 years) and less as a spouse (used to be 2 now 5) for time counting towards PR and thus by default citizenship. Its my opinion too that Parliament due to a weak RO obligation (2/5 years) wanted to prevent those PRs playing the RO roulette from applying for citizenship. Non PR time is not subject to the RO so getting rid of it is a useful tool to achieve this as also aided by the 183 days physical presence in each qualifying year requirement.