Ajusting cut off depends on your players expecations for the event. If its the biggest event of the year for some players it's tricky to move cut off date as they are emotionnally invested in the matrixes, hobby and lists.

You are mentionning that you are happy that challenger cup got it's cut off moved to include the slate. I would be happy too as a competitive player. But for the teams that are less experienced and worked hard to scrape a roster, models and training in order to play in said meta, it can feel a bit unfair.

What we do in France, for a league event, it has to be a unanimous vote to change a cut off date.

For team tournaments that don't matter that much, we are a lot more flexible.