Poor cultural practices a constant barrier
I have the same issues on the cultural end, over here in NJ and eastern PA most homeowners still struggle with the fact that if they refuse to water during the intense heat and weed pressures of summer the cool season grasses go dormant, thin out and sub come to invasion by C4 plants both grassy & broadleaf. The chemical barrier of a Pre-emergent will also be compromised by a thinning stand of turfgrass.
The other cultural issue ignored here and probably the largest one is mowing. Time and again the lawns are mowed too short putting them under severe stress by reducing canopy height and precious leaf tissue needed for transpiration and CO2 exchange. The shortened height reduces resistance to pathogen activity such as leaf, dollar spot and brown patch 3 common culprits.
I can see you deal with a lot of saturation and shade, 2 tough environmental/ cultural issues.
I just keep plugging along and educating the clients as I go, there will be some we never reach. My take on it is to keep being as proactive as possible catching the problems while they are small.