Before getting to the cockpit door, you would have a main door exit equipped with an evacuation slide on either side of you. If you tried to evacuate through the flight deck and the pilots were incapacitated it would be very difficult to clamber over them as cockpits are usually very cramped. On the B737, the entrance would be blocked if the jump seat was in use.
The emergency briefing doesn't include flight deck specific information so you may not know where the exit is or how to open it. Clambering down a rope, especially if injured is less preferable to simply jumping into a slide.
Flight deck escape routes are there in case we can't get out through the cabin as exiting will take longer and be more difficult.
In an emergency the pilots will want to ensure all the passengers have got off first before leaving.