There are plenty of reasons an individual may be looking for exercises to hit a specific muscle. I agree compound lifts are great for people interested in pursuing general fitness but there are plenty of people who can benefit from this.
I’ve used it because I needed to strengthen specific muscles after injuries or to protect from re-injury and wanted to explore options. I’ve also used it to mix up lifting routines by having multiple exercises I can rotate through that hit the same muscles. Clearly I’m a fan :)
Just like being in the gym, it’s important not to judge how others are working on their bodies^. You never know the story behind why someone is doing what they do.
^unless they’re putting themselves in honest to god danger of course!