It takes some time for a second leaf to develop. The second difference is leaf venation. Monocot leaves have parallel veins versus the branching veins of dicots. It is harder for plants with parallel veins to pump enough water to stay cool in the heat of summer. Hostas in the wild are found in wet rather than dry areas.
Branched veins are much better for transporting water.
The more water that can be transported, the more efficient the plant is at cooling the leaf surface. Plants transpire water through the stomatas as a cooling system. Cooler leaves and cells are more conducive to other plant processes, such as photosynthesis. Third is the root systems. Monocots have fibrous root systems while dicots have netted root systems.