Why did Texans want their independence from Mexico?

White Texans saw themselves as culturally American, not Mexican. They spoke English, not Spanish, and felt a much closer affinity with the United States than with Mexico. The stark cultural differences extended to the issue of slavery. Slavery was illegal in Mexico, yet the vast majority of white Texans supported the institution. Many American settlers coming into Texas had brought their slaves with them, and were reluctant to give them up.
As with the rest of the United States, slavery was closely linked to the wider issue of states' rights. The 1824 Mexican Constitution had granted the Texans a fair degree of control over their own affairs. Yet it was subsequently abolished by the Mexican government, which gave itself more power and control, much to the outrage of the Texan public. The abolition of the 1824 Constitution was indicative of the chronic instability of the Mexican political system. Texans increasingly felt that there was no one they could turn to in order to protect their interests. They certainly couldn't rely on the chaotic central administration in Mexico City with its rapid turnover of presidents.
In economic terms, Texas benefited little from being part of Mexico. Most of the state's trade was with the United States, and so inevitably, close economic ties developed. As with many parts of the South, cotton was a vitally important cash crop for Texas. But it was difficult to transport to Mexican territory on account of the vast tracts of arid desert that separated Texas from Mexico proper. It was much easier to transport cotton, as with most other goods, downstream to American ports such as New Orleans.