Oh I have seen a lot. The grand majority of them have two main problem areas, one from the early stage of development and one from the final stage.
For one thing, many custom maps were not planned right or not planned at all. Flags all over the place, no clear routes into combat areas (if they have designed combat areas at all). Some of these mappers seem to use the PR method of mapping, which results in maps that look very natural, but like they were created with a random map generator. Tournament maps tend to suffer from this, although there are some really nice ones and they often have clear routes.
There are also often scalability issues, meaning varying levels of scale and detail that maps look disjointed. To understand what I mean, compare the terrain and city layout of Meuse River and Operation Goodwood. These maps have completely different scales, but they are internally consistent. That is something most community maps (and some early official maps) fail at.
And that is not even counting people who clearly are just learning the basics of the technical side to mapping, where you get hand painted textures and vBF2 objects that fuck up texture loads.
The second big area is actually finishing the map: Creating final lightmaps, trench skirt textures, color correction, envmaps, ambient sounds, minimap, loadmap, music, map description in English and German, strings for game modes, deletion of trenchskirt shadows... show me one custom map with all these things in order.
Many people assume that "FH2 standards" means highly detailed maps with as many objects as possible, but that is wrong. Often inexperienced mapper place objects everywhere, lying in your way or right in your fucking face, but that is not a sign of quality. Every monkey with enough time can do that. Getting a map up to FH2 standards means the stuff I named above and more. None of it is especially hard to do, but it is boring, time consuming and many people don't know how it works. And no dev has the time or energy to explain it to some ding dong who might just give up and vanish the next day or do it on a custom map he didn't make himself.