Why did many Texas cattle ranchers engage in cattle drives to take their cattle to market elsewhere instead of selling them to Texas markets?

The Texas markets was controlled by the Spaniards.

Explanation:

The Spaniards had practically controlled the Cattle markets in The New world ever since mid 1500s. When they entered Texas, it is easy for the Spaniards to established a large operation while keeping the expense really low. This prevented the Texas Ranchers from gaining enough Revenue locally.

This is why they're engaged in "Cattle Drives". They're manually transporting their cattle from Texas to another states and sell the castles there.  (regions such as New Orleans / Missouri were the main destination for these ranchers)

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