It's a result of the second Quebec referendum. The Clarity Act may appear like it facilitates leaving the federation, but many critics (among them federalist and sovereigntists) believe that the law is too vague as it give the House of Commons the responsibility to determine "whether a clear majority had expressed itself". What that means in numerical terms? Nobody knows. Further the House of Commons has the right to override the referendum if they deem it to contradict any of the under-specified tenets of the Clarity act. Finally, you need to amend the Canadian constitution to finally separate, which according to my understanding, requires the approval of all the (remaining) provinces.

So it can be argued that the Clarity Act is a way to legislate friction to defederation.

Of course Quebec (and like Albertan) separatists hold that all this is moot and that they can self-govern as they wish following a referendum. Others look at the "no-deal" Brexit as a template.

> the law is too vague as it give the House of Commons the responsibility to determine "whether a clear majority had expressed itself"

If it really came down to it, i think it would be the supreme court that decides.