I can see where you are coming from @Ragnarolf, my theory would...

I can see where you are coming from @Ragnarolf, my theory would be that they already have fast track with the MAST trial and they have gone through multiple cohorts to get to what would appear to be very close to RP2D.
Clearly OASIS is the main game as it opens up 90% of cancer market with the inclusion of CD19 targeting treatments, they may not have the funds and may have trouble recruiting enough patients to run what is effectively a parallel trial.
Gaining fast track designation for the OASIS trial will open up some eyes to what could be achieved in quick time, if a particular cancer could return brilliant results.
This does not mean the MAST trial is dead in the water, I am hopeful of some good data still to be revealed in the cominig months.
We need to remember that this is a fast moving beast as many of the changes in direction have indicated, the Company is in an extremely competitive environement and needs to be able to change shape to continue to keep up, even to lead with break through therapies.
While I may not like some of the decisions made, I do not have the gual to think I know better than the very experienced and professional people they have on board with whom I have great faith.
This may cost me a lot of money at the end of the day, or alternatively it will be a Company that my Great Grandchildren talk about in years to come, only time will reveal this story.

DYOR opinion only