Why/Does it take less force to unplug the cable if you pull it at a bigger lengths? I've tried many times and it seems so.
This is the same reason why longer screwdrivers are said to "produce more torque" when driving a screw. For the same angular deviation from the optimal axis, the longer the wire/screwdriver is, the more the deviation in distance from that optimal line.
That means with a longer screwdriver/wire, angular alignment is less sensitive to hand position while misalignment is also easier to detect. Pay very close attention to the exact motion, angles, and directions of your arm, hands, and fingers when pulling the cable out. Also, remember that the laptop port sits closer to the surface of the table than your hand is thick, and both your eyes and arms high above. Your misalignment is probably more up than sideways. Sideways misalignment is not the only misalignment possible; It's just the most visible from your eyes above.
At 2cm length, you might be pulling at 30 degrees and not notice. You would never do that when pulling at 30cm.
Another contributing cause is that the longer cable length results in a longer motion, if the cable is not taut when you start pulling - the hand, and the end of the cable have more time to accelerate. That is also why it is harder to put force in a short punch.
As Amit mentioned in their comment, depending on the proportion of the cable+connector assembly that is rigid - shorter rigid part decreases the contribution of pulling at an angle as the moment becomes smaller - the cable pulling at an angle creates a sideways force on the connector, which is larger the longer cable is as well as this effectively becomes a system of two levers once the cable is pulled taut.
There may also be an extra side effect, as the connector being pulled sideways causes it to jam against the socket, with more friction to overcome to pull this out. If the rigid part is short or nonexistent, both of those angle-based effects are a lot less pronounced, the angle still likely plays a part though, as determined by the vector math (which I am not good at) of forces involved.
I would suggest that the difference in force is just an illusion. If your hand grabs the cord from close up to the laptop, you're probably using minor muscles to pull the cord out. But if your hand grabs the cord from farther out and you pull, you're probably using major muscles to pull the cord out.
It will actually take slightly more force to unplug a cable when the length is longer.
This is because the cable will stretch to some extent as it is pulled, even if that stretch is very minimal. The longer the cable, the more material there is to be stretched.
Note: This same stretch may make it feel like it takes less force to unplug a longer cable than a shorter one. As force is applied to the cable, it stretches, and then contracts. Thus the cable itself is "helping" to unplug the end from the socket.
If a force gauge were applied consistently to this question, I believe we would find that it takes more force to unplug a longer cable than a shorter one.
This is assuming a steady pull. If we're talking about a quick "yank" instead, then the stretch mentioned above might cause the longer cable to unplug with less force, due to the contraction of the cable after the yank. But some energy is going to be lost to friction, so even taking this into account the longer cable should still require more force to be unplugged.