I was complaining about them for a long time when we first got them at our store about 6 months ago. You just have to learn to drive them all over again with the cart pusher. I liked the older, heavier styles so much better because they drove in a straight line, but now I don't complain, I just got used to them. Don't push more than 7 at a time by hand, or your you can get in trouble. When I train new cart attendants, I start them off on about 12 or 14 with the cart pusher at a time and no more.
The new lighter carts are lighter, wider, and ride only on the front wheels when you have them linked together. Therefore there is nothing to keep them stationary if the wind kicks up since the front wheels they are riding on spin in any direction (they actually act like a sail if you have too many on there and can snap from side to side if you try to take to many). Just practice and over time you will get used to it. I've heard of other CA's using ropes and stuff. I don't. Go to an empty part of the parking lot and try snapping that front cart around and seeing how the carts react. I just had to learn when to snap the front cart in a different direction, how to drive that front cart to make my carts go straight, etc. Now I push 25 - 30 with ease unless the wind is gusting. If you have an old style cart on the pusher, have the sft install one of the new styles on there. It made a world of difference for us just fyi.
Bottom line, start out small and work your way up with the pusher. It only takes me 15 minutes now to get every cart out of our parking lot in 2 runs.