Why the hell the B-57B (nuke) spawn on airfield

Why the B-52B spawns on airfield it cannot lift up from it

Because all nuke planes do…
Also it can lift up, you’re just not at its rotation speed.
You’re trying to lift up prior to getting up to speed, which is causing it to not get up to speed thus not lifting.
Brakes on, engines spooled, brakes off after 10 - 20 seconds, flaps down above 230kph, lift off.

it’s ground RB