That's probably because you need lots of work on your macro. The entire reason Z is so good on those maps is because it's easy to get away with expanding / droning. Maps like steps of war are are like one skip to your nat for tanks / terran.
One of my recent games I did quite the opposite. I concentrated on my macro and started getting upgrades, etc.... I had 55 drones on 3 bases, 2 of them somewhat saturated and the 3rd I was getting gas and a couple of drones were mining. I scouted his base with some forces massed, so, I made some units(hydras+roaches) and decided to mass slings to do a quick attack since I had a lot of resources. Turns out he decided to attack just then and I realized it a little too late, so, I wasn't able to mass units and I lost