Because I'm lazy :) ha ha. I guess the heavy jig just suits my style more because I can pitch it farther and keep a better connection with the bait. I will use a 3/8 or 1/2 sometimes but unless I'm fishing really slow, it's harder for me to feel the lighter jig, especially on 20 and 25lb test line. I would say also that only maybe 1 bite in 15 comes on the initial fall of the jig for me. Every once and a while I get that bite where you pitch in and the fish on there, but most times I get bit along the bottom. So in my mind I figure if I'm getting bit along the bottom, why not just use a heavier jig?

I also do a lot of sort of long range pitching where I pitch or sidearm the jig 50 to 80 feet. It's pretty easy to do with 5/8oz jigs but harder to control with 3/8. Seems like a lot of my bigger fish on jigs have come making long pitches and I think it has to do with that I'm not spooking the fish by getting right on top of them and trying to flip for them.