The deadline portion come in when someone expects to pay for the work or to pay for the opportunity cost for the work not being completed...

And that someone usually needs to get some information to me by a certain time for my estimate to be reliable, and often doesn't. Or they need to not change the plan half way through and expect the same delivery time. Or needs to understand that when I say two tasks will take about a day each, no I can have both done by tomorrow. And do on, and so forth.

And yet Deloitte continues to exist and overcharge and overrun deadlines, and the economy, I'm told, is still doing quite well. Maybe this is all kayfabe and it doesn't actually matter.