The unfortunate fact here in Illinois is, the only people who can afford to belong to the legislature are attorneys. State House races in the Chicago area can cost several hundred thousand dollars, to "win" a job that pays about $35,000 annually.
This may be true in many states. The pay for a State Representative is quite low -- it was never meant to be a full-time job -- and the hours are quite long -- what was supposed to be a part-time job three months a year has blossomed into a career, with many state legislatures meeting year-round. When the legislature isn't in session, the rep is usually out meeting with constituents, spending time in his district office(s) (if he has a large area as his district, he may have offices in several counties), or campaigning. That doesn't leave a lot of time for earning money to support himself.
A lawyer can be a partner in a firm, and the firm subsidizes his legislative efforts because it's nice to have political connections if you deal with any state industries. Of all the state reps in Illinois, I can only think of one who is not an attorney. He's the oldest son of a family who owns a real-estate and construction firm. They ran him for State Representative because he was such a scr*w-up he was costing the business money and they wanted to get him out of the way (He's my State Senator now. Lucky me.)