If your not charging by the hour then you would not be making the same per hour. Maybe it is how you estimate your jobs that it ends up like that?
Here on septic I may profit 1500 dollars for 2 days. Laying sod I can profit 2000.00 in one day. Throw in some stone work, drainage , plants , irrigation and I can quadruple my profit per day over septic. The septic is steady year round and pays the bills.