Thing is, the money he gives to his mother is NOTHING to him.
She lives in Yonkers, not Central Park West overlooking the Park. Even though that was a McMansion, it could be in his name or she's going to leave it to him or other family members if she passes.
Maybe there's housekeeping, maybe someone comes and cooks for her. And when she needs help when she's older, he could hire some nurse to help her or move her into a fancy retirement home.
All that cost is probably not even 1% of his annual income for a "deca."
OK so he's going to cut her off, go to some retirement home for people on Medicaid? You know, the nursing homes which are raging with the corona virus thees days?
He was worried about adverse publicity from not showing up for that Yonkers dinner, how is it going to look when stories come out that "deca" Bobby Axelrod put his mother out on the streets?
Now maybe she's given his father money in the past. He was probably suspicious when he didn't see the car he bought her in the driveway.
But what's at issue is not money. He barely notices it going to his mother and who cares if she gives some of it to his father? She probably figures it's nothing to Axe and sees no reason her ex has to deal with buses.
For Bobby, it's about punishing him and then if she doesn't bend to his will, punishing her too, though I think it wouldn't be too long before Wendy points out it's not a smart PR move, especially when he's trying to get a bank which requires govt. agencies approving.
That's why he yelled at her, because he's a petulant prick who was threatening to take his ball and go home when things don't go his way.
You can take the boy out of Yonkers but you can't take Yonkers out of the boy.