Why is it so much easier to ditch a prime minister in the U.K. than in Canada?

Despite having nearly identical parliamentary systems, Canada has avoided the kind of prime ministerial parade that has befallen the U.K. in the past decade. Political watchers point to the Brexit vote as the key moment that led to half a dozen leaders occupying 10 Downing Street in the 10 years since, but there are underlying factors that make it easier for U.K. MPs to ditch a leader than their Canadian counterparts.