Mmmm,
I would say wargames are not necessarily more complex per se than many euros. They tend not to have too many interlocking systems and most of them, even “complex” ones, have decision loops that boil down to move-and-shoot, where de difficulty lies on choosing between the huge amount of options (in my personal opinion wargames tend to encourage “statistical” thinking, where single moves become less important than overall strategies -compounded by the heavy reliance in random tables-).
What wargames are is granular. Where a more mainstream wargame would have 10 pieces, wargames give you 100-200. Where a stat would have 3 levels (good, neutral and bad), wargames give you strength numbers in something like 10-20 different overall values. And this granularity is a big part of the UI clutter in the genre.
I think from a pure game design standpoint the granularity is not necessary, and there are successful designs that have done away with it, but in general, the wargame market reacts poorly to granularity simplifications.
I think part of it has to do with the perception (or sales pitch) that these games are also simulations (I would say many of them are at the very least “studies” on different situations and theories of warfare), so limiting the granularity does impact the “precision” of the simulation so to speak.
This ties to an area where wargames are definitely “complex”, and that’s the rulebook, or the extremely process heavy nature of playing. Since for example, a wargame has to adhere to a theory on how to model losses, and due to the extreme granularity, you have stuff like counting factors, etc…
But yeah, other than the granularity problem, which I don’t think it’s easily solvable unless you can simplify individual outcomes (and again, that’s a hard sell for a lot of the target market), a lot of the other issues are indeed solvable and there are nice attempts here and there (I love the Enemy Action series chit pulling for damage calculation, which avoids both the need to consult a CRT and also to calculate modifiers. At most you need to add factors).
In general I agree wargame UI can be vastly improved and that there’s a lot of inertia in there, but that’s both designer and buyer inertia. I just don’t know if those games with clearer UI will sell great if they lose granularity (and I don’t know how you solve stacking while maintaining granularity).
But there’s stuff like this out there: Helsinki 1918: German Intervention in the Finnish Civil War | Board Game | BoardGameGeek