They will do this because there will always be more money in some other location than Oakland, especially as long as the NFL is leaving Los Angeles fallow. (See Clippers, LA, the sale thereof.)
There is no financial penalty to the Raiders for doing this.
There is no one in the Bay Area that makes the decision to go to a game, buy the merch, or tune in the telecast based on whether or not the organization has been petulant asshats.
This is because every NFL franchise is on a continuum of moral bankruptcy and degeneracy, and everyone knows that before they turn on the game, and they turn on the game anyway, because junkies are not picky.
In a better country and system, there would be relegation and promotion to prevent the wanton abuse of a fan base by repellent and incompetent ownership.
In a less better country and system, there would be regulation -- because every franchise is sucking public money in some fashion, and a concentrated federal and state action would attack Oakland's league partners, and use that leverage to coerce the Raiders out of extortion.
In an even less better country and system, taxpayers would rise up and vote out each and every political official that funnels taxpayer money to private and wildly profitable sports monopolies, to the point where people who run for office would no sooner be seen with athletes or owners than they would with pedophiles and reality television celebrities.
We live in none of these things, so please enjoy the continued do-se-do where the Raiders, Rams, Chargers and any other franchise with a financial itch to scratch tries to get to the cash register with the gun and the bandanna first.
No team needs the money, and neither do any of the ownership groups.
And if and when one of them breaks through and cashes in...
You will know just how corrupt and abhorrent the media is by those that choose to tell you how wonderful the new venue is, and how many people in Los Angeles are just so happy to have football again...