There are many obstacles with states trying to legalize sports betting, however it is much harder for a state which was not exempt from the "Bradley Act" as is the case with Illinois. I have listed below some info about the Bradley Act which can be found on Wikipedia:

The Professional and Amateur Sports Protection Act of 1992 (Pub.L. 102-559), also known as the "Bradley Act," attempts to define the legal status of sports betting throughout the United States. This act effectively outlawed sports betting nationwide, excluding a few states.

The sports lotteries conducted in Oregon, Delaware, and Montana were exempt, as well as the licensed sports pools in Nevada. In addition, Congress provided a one-year window of opportunity from the effective date of PASPA (January 1, 1993) for states which operated licensed casino gaming for the previous ten-year period to pass laws permitting sports wagering. The latter exception was clearly crafted with New Jersey in mind. However, New Jersey failed to take advantage of this opportunity and carve out an exception for itself. Also excluded from the reach of PASPA are jai alai and parimutuel horse and dog racing.
[edit] Legal Challenges

As part of a widespread trend to legalize, regulate, and tax sports to increase tax revenues, many states are trying to persuade the federal government to repeal PASPA. Proponents of repeal typically assert that the law as written is inherently unconstitutional, as the US constitution reserves to the states all rights not explicitly granted to the Federal government -- such as gambling regulation.

BoL,