Because it's hard. You've got a career, a family, outside interests, etc.
When you step back to look at what the average working professional does, it's incredibly hard. Nothing usually comes with ease.
Which brings me to the reason interviewing for empathy is so important - Are you someone that's mature enough to understand that, or are you the first to brutally bitch and criticize rather than slow down and understand what it's like to walk in someone else's shoes?
There's got to be some empathy for how hard it is to generate results in roles other than your own if you're going to be an effective teammate. Or an effective coach of people. It doesn't mean you can't coach for performance or hold people accountable. It's a worldview. It's a pre-requisite to accountability.
So interview for empathy in your next interview. Ask them about a team member who let them down. Wind them up and let them talk - and figure out if they're a potential team member or just another shark looking for a meal.