In some cases, it’s because the cost of letting them go and hiring+training another individual is daunting. Both monetarily and in time. You also don’t know if the new hire will necessarily be better. There’s also other factors like firing someone doesn’t necessarily get you back a headcount immediately. Visa caps also play into this because for certain roles we legitimately could not find enough candidates locally, so letting someone go means you couldn’t find someone till the following year.

I’ve been in this situation where I’ve had to convince my managers that the teams I managed would be better served without certain individuals and I’d rather hire someone new. Even when the entire management chain agreed, it came down to the issues above.