This is rare in politics as most are wont to pursue ambition and career and thus ( in our parliamentary/cabinet. fusion of power system), defend policies and decisions of cabinet/government that clash with their values/principles.
She could not and thus her resignation ......" in Canada, the constitutional convention of cabinet solidarity means, among other things, that ministers are expected to defend all cabinet decisions. A minister must always e prepared to defend other ministers publiclty, and must speak in support of the government and its policies"......." Given this convention and the current circumstances, it is untenable for me to continue to serve as a Cabinet minister".
Untenable, because of the pressure put on fellow minister, Wilson-Raybould and " the independence and integrity of our justice system". Philpott and JSR had worked closely on a variety of issues like assisted dying and cannabis bills and had formed a mutual respect club and had become friends ( Philpott thanked JWR on helping her understand and improve her understanding of First Nations issues).
From all reports, Philpott was one of the most competent minister, greatly respected by her colleagues and Trudeau ( unlike in the JWR, case), noted that that and praised her service.
Why did he not praise and thank JSW? For one, she stood up to him, confronted him, turned away pressure from PMO and PCO and others and withstood the whispering,( racist, sexist, personal...she's arrogant, not a team player, taking advice from her father etc.), campaign, on the deferred, remedial arrangement with SNC. She chose not to resign, forcing Trudeau's hand, and he had to shuffle out of her position and demoted her to Veterans Affairs ( there have bee 5 ministers so far, treated as a dumping ground... no respect for Veterans, it would seem).
Then she resigned . Why now? It was because now as Veterans minister she would have to be a team player agreeing with all that the government and Cabinet decide and she could not do that ( as AG, she protected the Rule of Law, independent of her position as Justice minister...she did not have to be a team player but and independent actor).
This is what Philpott is saying with her resignation...she could not support Cabinet positions as required ...." all for one and one for all" principle of Cabinet Unity and Solidarity.
So here we are, with Trudeau and the Liberals caught in whirlpool of their own making, that threatens to ring down the government. This matter could have been resolved by simply coming out and stating their case about the need to allow SNC make a deal. They could have sold it easily, given the importance of SNC, the need to compete with other corporations of US, UK, etc. who have laws allowing for deferred prosecution. Instead Trudeau tried to play ard all with a principled minister who took er job as Attorney General and protecting the integrity of the very seriously
This is the first time in recent years that a Minister has resigned on principle. This takes character and integrity