I totally agree about companies specking short droppers all the time. What’s the point of a shirt seat tube/standover if you have to run 50mm of seatpost out of your frame? Surely it’s better to spec the longest you can sensibly get away with (for the rider height you expect) and if there’s the odd person who might want a short one it’s cheaper for them to swap it.
On my 2021 5010, Large, I’ve probably got 80-90mm of my 170mm dropper out of the frame.
Yes I could fit 170mm dropper to full insertion, but could I fit a theoretical 250 at full insertion with the tunnel for the shock?
However I’m going to mainly blame aesthetics. One of my rules for pretty bikes is that top tube should be 90 degrees to the fork. For any given head angle and fork length this sets where the top tube will end up – with a bit of a seat mast/brace added on top for stiffness.