I always thought it was because golf didn't as well. I also thought golf didn't allow them because judging conditions was an aspect of the skill of golf.
When golf started to allow rangefinders, the reasoning was that because distance was fixed, all players could have access to that information anyway from Yardage Charts. So, it was no longer a test of skill.
Golf still doesn't allow devices that measure other things like wind speed and slope (at some levels of competition). Those still test the skill of the player to judge conditions.
Which makes me wonder if disc golf should disallow wind gauges.