Because they work for companies where the product would fail within days of them being fired themselves.
Because they work for companies where the product would fail within days of them being fired themselves.
I worked at a company where everything hinged solely on one guy working from another country. When he left, loss of institutional knowledge took about three days to show real effects as things also came down crashing.
I worked hard to make _myself_ replaceable for when I left, it was a pretty good exercise, but me having that degree of freedom was symptomatic of the problems of the company.
The truth in retrospect is that it was my fault (and my upper leadership's) that I wasn't replaceable. I created a knowledge silo around myself since I wanted to move fast and figured I could prevent the team from being bogged down in complexity if I just handled it myself and while that worked in regards to delivering out-sized results for the available bandwidth, it also was a risk that materialized as described above. So while I do believe that everyone should be replaceable and it's their responsibility to be, it's not always the case and products can live and die by it.
That said you can replace people and build back that institutional knowledge -- both loss and gain take significant amount of time.
For the type of jobs at hand here, One of the things I learned is that nobody is essential. Even that person you think is essential.