That disgruntled Liberal members of Parliament lack the ability to remove their leader is entirely their own fault. It is they who decided to deny themselves the ability to do so.

Fairly late into its decade in government, Stephen Harper’s Conservatives passed something called the Reform Act. Introduced as an amendment to the Parliament of Canada Act as a private members bill by Conservative MP Michael Chong, its purpose was to enhance the power and influence of MPs, ensure none of them could be evicted from their caucus without the approval of their peers and—most important—grant them the power to remove their party leader.
It also, unfortunately, made signing on to the provisions optional for all parties. Only the Conservatives chose to do so and, indeed, they used it to remove their previous leader, Erin O’Toole, following the 2021 election. The bill allows for MPs to petition for a confidence vote on their leader which, in Mr. O’Toole’s case, resulted in a thumbs down, the appointment of an interim, and a vote by party members for a new leader—in this case Pierre Poilievre.