What is at stake is the survival of the yellow-green network of people who used to control all agencies, as well as the judiciary, by appointing each other. All these positions are based on reciprocal appointments or approval by the judiciary, the agencies and the Senate.
As this network has lost most of its electoral base, in particular in Bangkok which has largely switched to MFP, this is clearly a survival issue.
Concerning the Senate:
"4. Providing advice or approving an appointment of a person to
hold a position
The Constitution provides duties and powers of the Senate in giving
approval to a person for holding positions in organs under the Constitution,
namely Judge of the Constitutional Court, Election Commissioner, Ombudsman, Member of the National Anti-Corruption Commission, Member of the State Audit Commission, Auditor-General and Member of the National Human Rights Commission who are elected or selected by the Selection Committee."
https://www.senate.go.th/assets/portals/1/fileups/419/files/senate Eng.pdf