Is the reason why barometers are screwed to the bulkhead and not mounted near the navigation desk:
-bulkhead is less susceptible to pressure fluctuations away from companionway?
-closer to centroid of yacht therefore needs less damping?
-designers place the barometer over the main cabin sea berths so you can drip from your foulies on sleeping crew when trying to read it?
- some other reason that I haven't thought of.

I want to relocate mine to the nav desk so I can easily update the log. Why is this not the typical spot?

No reason other than decoration.... And Sitting in your saloon totally baked out by the sun because you don't have a Bimini.., your brain is fried and you suddenly get up with an urge to tinker and what better than a barometer placed strategically on the saloon bulk head to get you on your feet for a little tap,tap aroo,,, it keeps your fried brain from messing around at the chart table for a few minutes whilst the last slug on the warm emu bitter brings you around like a parametric with smelling salts
By all means,,, mount the barometer at the chart table.

EastCoastSail said..
Is the reason why barometers are screwed to the bulkhead and not mounted near the navigation desk:
-bulkhead is less susceptible to pressure fluctuations away from companionway?

That is the reason. A lot of Nav stations are close to the companionway which will suffer from different pressures caused by constant wind or even gusts. The barometer will be inaccurate.
I still use analog weather stations, charts and old navigational tools. Never know when digital will let you down, offshore.