For some reason not many people like the "maintenance" type of work.
Even more so in a lot of orgs maintenance work gets hit by the "cost center" mentality and management only rewards not hearing about it.
I can do about 4-5 hours a day of "difficult" programming, but then I can easily do another 4-5 hours of this maintenance type work, and the cumulative effects of repeated maintenance time keeps everything running super smoothly.
Why bother?
Even if the whole project has no career purpose, it's more fun to write new code.
So things can be largely a question of perspective.
It's also nice that bug chasing has less of an expectation of giving good times estimates, which the software industry is famously poor at anyway.