Mostly the same. I have had two ex-coworkers who said they were leaving for the pay raise, but were both clearly unhappy with their jobs prior to leaving. I suspect "I wanted a raise" is just a much easier reason to tell people than "I hated the people I worked with", especially when it's the people you worked with asking.
Hmm, for me it always comes down to “I don’t get paid enough for this shit.” They can then reduce the amount of shit, or increase the amount I’m being paid.
If some other company wants to pay me more for the same shit, then that is where we are going.
This is it. Everyone's line of what they're willing to deal with is different, and changes based on where they are in life, what their mood is that month/week/day, etc. It only takes so many days of crossing that threshold for someone to start looking around.
If a job is crappy in general, the pay is likely to be part of the crappiness. Or from the other side of the yin-yang, part of what can make a better job better is better pay.