There's a techniuqe i like, I think it's a Lean technique, anyways it's called 5 Why's. When ever I get to act as a filter on requirements from the business, I bust it out to tease out the root cause issues driving the solution. It's really good.

Essentially it boils down to asking Why as much as possible until you get to the original problem. From there the problem can be put in the backlog to be solved by the devs rather than the precooked solution.

The author has a complementary article that addresses that: https://lethain.com/limiting-wip/.

Exactly. When you are adding items to backlog faster than the team can process them, it is not obvious to me why "add more people to the team" should be the right solution.

Maybe there was a wrong decision made at the beginning of the project that needs to be fixed. Maybe the version 1.0 has too many features. Maybe the project could be split in two independent parts (which will still require hiring more people, but with less complex of internal communication). Maybe the basic infrastructure was not set up correctly (logging, unit tests, continuous integration) and there is no time to make it right because the visible parts of the application always get the top priority. Maybe the team members are working with a technology they never used before, and giving them a one-week training could increase their speed dramatically. Maybe there is some interpersonal conflict in the team, where things could be improved by removing a team member?

More importantly, why are you adding new items to the backlog so fast? Is your company doing "agile rituals, but with predetermined scope and deadlines"?

Let me guess: the answer "hire more people" is so popular, because it is a universal answer that does not require the manager to actually understand anything; and as a nice side effect, having more underlings increases the manager's importance.