CBS considers the Star Trek brand reliable. Currently, DIS is the standard-bearer. They're not going to axe their flagship show. But the fact that they're retooling it again also implies the actual numbers - whatever they may be - where below expectations. Which can also be the result of unrealistic expectations *cough Beyond *cough
But in general, every show where people have to tell everyone how it's the biggest, most watched Nr. 1 show, and have to rely on really obscure and indirect sources for that claim - simply isn't. Doesn't mean it's not successfull mind you.
*yawn* They're retooling it in the same way that Shore Leave was a retooling of Star Trek after Balance of terror. Is it going to be 'retooled again' when season 4 is a different story too (you know, like The Galileo Seven was after Shore leave)? But I'm sure that after 7 seasons there will be people saying it fell below the expectations of CBS *somehow*.