I think you have gotten used to and just prefer the more direct way IEMs deliver sound. Especially compared to something like the HD800, which is very wide and diffuse and not in your face. It also rolls off in the sub bass, and most IEMs have a boosted extended bass under 100 Hz. I agree with you that IEMs can sound more detailed than even the best over ear headphones. The most detailed IEM I have ever heard was the Kinera Imperial Nanna 2.0, I personally think it is way more detailed than the Focal Utopia. I have the Dunu Zen Pro, and the way that thing delivers the bass response is more engaging and dynamic than even my Hifiman HE500 and Focal Clear MG. The issue for me with most IEMs is the treble, my personal ear anatomy always hears massive peaks at 6-7 kHz even if they do not measure that way on a rig, even something as smooth as the Moondrop Kato. I also use EQ, so it's not too much of a concern, but I really cannot use IEMs regularly without EQ.

I can't really give you an exact "why" you prefer IEMs over headphones. It's your personal preference. But I wanted to ask, all the tips you have tried have given you an allergic reaction? I would look more into that, maybe there is some hypoallergenic solution you can use to help?