Why is the Texas governor's power exceptionally weak as compared to that of the governors of some other states?

Due to Article 4 of Texas Constitution.

Explanation:

According to Article 4 of Texas Constitution Texas has plural executive. It means that Governor's power are limited by distributing it amongst other government officials. No one government official is solely responsible for the Texas executive instead there are more than one officer.

Texas executive is known as plural executive. The taxas executive involves Lieutenant Governor, Attorney General, secretary of State, Commissioner of General Land Office, controller of Public accounts and other members of Texas plural executive, due to this Texas governor's power is weak as compared to other governers.