From the article you will see that this question was addressed and the answer seems perfectly reasonable to me.
The Schindlers - who did not respond to a request for an interview made through their lawyer - have been distrustful of his motives partly because, they have said, no one mentioned Terri's wishes until years after her collapse. But, Scott said, "it's not something you think about while Mike's trying to save her life... . It's something that people do when there's nothing left to do."
It's because of his testimony in the lawsuit.
It's because of his treatment of her. Contrary to his claims of how well he treated her, the preponderance of evidence indicates he despised her, and wanted her dead quite soon after he got the lawsuit settlement.
Those witnesses, volunteered to give their affidavits, and they have absolutely nothing to gain.
Michael has money, remarrying, no time out to have to deal with Terri, or the Lawyer, or the media.
He has contradicted himself, and tried to blame everyone else for 'his problems'.
He keeps her room dark and cold, has had personal effects removed.
He doesn't want her given water by mouth as she may choke to death.
At least it would me more merciful than dehydrating and starving her to death over a likely two week period.