"What's a lame duck president to gain from it?"
You're asking that, seriously?
It's not complex. GWB has rich and powerful friends. The rich and powerful tend to be business owners. Now, if you employed 10,000 people making widgets, would you rather pay them $8/hour, or $4/hour?
Illegals work cheaper, and many are off the books, so no other benefits are required.
GWB helps the rich and powerful, and in return GWB will be rewarded. That's politics.
You think Bush is expecting some kind of payola? I bash Bush regularly, but it's never occurred to me that he might be corrupt. Naive and misguided, yes, but I'm not ready to cross that bridge.