I have similar problems. For me it's primarily the spots I can focus on and time. When I go to smaller lakes and ponds, I'm only there to fish. The fishing is always easier on smaller bodies of water, but you can make the most of big lakes too. I'm relegated to short spurts of dock fishing and a few casts here and there from a party barge on the big lake because I'm there with family for leisure activities, not fishing.
The problem with larger lakes is the fish have a lot more room to spread out, so location is key. The dock I fish from is loaded with bluegill the kids can catch all day, but it is very rare to catch a bass there. There's really just not much cover other than the dock itself, the lake bottom is rocky and drops off fairly quick with hardly any cover. To attack the bass, I need to go to small coves with a lot of structure or the mouths of creeks that flow into it. There are a lot of bass tournaments on the large lake I go to and they do pretty well. Given a choice, I would rather fish the small lakes and ponds, so if I do have the time to spend, I'm not going to the large lake, therefore my success isn't that great there. If I was stuck there and had the time, I'd attack very specific spots with the best vegetation and cover away from the rocky barren shoreline.