I’m a bit skeptical about the implicit premise, that some people don’t have ideas and others do (as stated — clearly some people are simply more imaginative or creative than others.)
I suspect that what happens more often than not though is that people are self editing. They have ideas, and they dismiss them as fleeting or stupid — or fail even to distinguish that they are ideas rather than passing thoughts. We are our own worst critics.
The other thing that seems to be a play in the reality that some people are literal fonts of ideation and others baffen deserts, is that there are inadequate constraints on their attempts. When you set out to come up with an idea, in the absence of any significant constraints or an acknowledged problem, there’s nothing ‘against which’ to innovate . Innovation requires a substrate of constraint to flourish. There have to be problems with existing solutions, or seemingly intransigent problems in need of solutions — and sufficient constraints on possible solutions. Then the mind reels with imaginative ideas.