Why do wheat plants grow faster than bean plants?
It would be formal to compare the growth of plants in terms of types of their cotyledon they have: Monocots and dicots. Wheat is monocots and beans are dicots.
Monocots in general are faster to grow than the dicots. The main reason for this is their structure and support. Monocots are not as complicated in structural formation as compared to dicots. Meaning, dicots invest much in formation of trunks, wood and vascular system.
Since wheat is monocots and beans are dicots, wheat tends to grow faster than beans.