Large organizations are, for the most part, slow to change, and they tend to treat all "talent" in a similar way. They've been able to get away with this for technical talent for some time because the grass wasn't greener on the other side. Now, and for the foreseeable future, it will be.
Many large organizations (in my limited experience having worked for two non-tech focused Fortune 100s) value years experience over real experience and talent, have a stratified (and slow) system for promotions, are wary of young people making critical decisions, are not meritocracies, and are not really champions of the methodologies/technologies that most of the startup world has adopted for years. Each of these things are working against them in a major way.
In short, it's about more than the paycheck, and in the current environment that's especially true. Large corporations have to be willing to adapt and make the changes necessary to adapt to this fact, but their slow moving and old school cultures won't allow it. It's going to require a change from the ground up, and only the most progressive organizations will embrace this fact. But, then again, if they're progressive, then they're probably one of the few that don't need to worry about this issue.