The CRA tends to attract people looking for a safe job who happily accept  that in exchange for the lack of opportunities for advancement to a role like, say,  a VP of Tax of a large corporation and the high potential earnings that would come with it.  As a result, CRA auditors tend to go after low hanging fruit eg ask for birth certificates to support those child arts and fitness credits (gone after 2016).  They waste taxpayers' time on small amounts and generally just run the clock instead of trying to go after big cheats, since that would require more work, like compiling and analyzing several years of tax returns together.