Do politicians in the U.S. and especially Texas have much incentive to represent the interests of the poor?
Not all politicians are the same, of course, and some truly do seek elected office so that they can achieve positive change and represent their constituents. This is especially true at the local and state levels.
The farther up the line you go, say to the House or Senate, for example, the harder it is to represent the interests of the poor anywhere, including Texas. This is because of the millions of dollars necessary to be re-elected. A congressperson is constantly fundraising, and often ends up in political bed with lobbyists and industry so that not only do they continue to get donations, but their opponents do not. This leaves them beholden to business interests that are often at odds with the needs of poor Americans. That is, they are extrinsically motivated to help the wealthy. To help the poor would require intrinsic motivation simply to do good.
It's not a new problem, as money has been corrupting politics, the process and politicians for a very long time in the US, and the recent Supreme Court ruling in the Citizens United case has made the problem worse, not better.
There are notable exceptions with some elected officials, depending on your point of view, or what you classify as looking out for the poor. It's a good reason to get to know the candidates seeking office and what their positions are, as opposed to simply voting for the name that is familiar.