The case is set for a trial on May 6.
In Hollywood, deals are often verbal and not contractual but that did not impress the judge.
It was added that Bloom - who was let go by Depp in 2017 - was paid based on a percentage of the actor's earnings.
The Rum Diary star tried to sue Bloom in October saying their fees were on a "contingency basis."
Under California law, that type of fee system must be in writing.
Bloom countersued, stating the actor "failed to fully pay his legal bills and had violated the unwritten agreement."
Judge Green then reminded the court that the law is the law - the fee arrangement must be in writing.
"There's not a special rule for entertainment people," Green said Tuesday.
"Why isn't it in writing? Why not have something that memorialises the agreement so we don't end up in court fighting like this?"
Bloom's attorney said this type of fee arrangement is "common" in Hollywood.
Green then explained that he is familiar with the way people do things in Hollywood but is also "aware that showbiz people think they live in a different universe, but they don't. They're not a different universe."
He added that the fee should not be a percentage of what Depp earns because no one could have predicted how little or much he would make.
Bloom's attorneys may seek to appeal the judge's ruling.
