This is a piece of satirical verse, so you would be wise not to take everything literally.
The satire goes like this:
- Everybody agrees that the days of Good Queen Bess (Queen Elizabeth I, a beloved monarch) were golden.
- In the court of King James, who succeeded her, the court poets and the court gallants (whose livelihood depended on the King's patronage) would not dream of saying that King James' days were less 'golden' than the previous monarch. For that reason the days "could not be less" than golden.