Why?
Willing to bet the 'dislike' is "we have lots of mismashed, disorganized stacks, and expect seniors to have 20 years experience with all of them." coupled with "Even though some tools/stacks/etc have only been around 3 years."
And... even though a senior can pick up a stack in a few days, the expectation is to find someone already skilled.
....
Here's the truth. When I walk onto a new jobsite, I typically don't even know the tech. I've worked for EDA companies, government departments, startups, geospatial corps, all sorts of new and antiquated stacks and tech.
I'm a senior, and I can walk in, and become the subject expert extremely fast. I do so all the time, it's why people hire me.
That's what being an actual senior means. Loads of market experience, which makes that learning curve flatten.
$5 says the 'dislike' is an expectation that stuff can't be learned fast. I'd scoff.