Why do people use brokerage accounts for savings instead of a CMA?

In a previous post, I noticed that a lot of people seem to use a brokerage account as a sort of savings account instead of a cash management account (CMA).

Is there any downside or catch to doing that?

I always thought you could just use something like SPAXX as the core position in a CMA and basically get the same effect. Am I missing something here, or is it just preference/convenience?