Is there any convincing argument which could explain why disregard for Church law might be confined to Holy Thursday liturgies and not spread to others matters ecclesiastical?
No.
He is making a fool out of all those loyal Catholics who have bent over backwards to try to put a good spin on all his statements and deeds over the past year.
A couple weeks ago I was visiting my parents, and there was a picture of Pope Francis on the news channel. My 79 yo mom said to me, "What do you think of this Pope?"
I simply responded, "I don't trust him."
She thought that was a shame. Indeed it is.