Management does not understand what a "3-4" workload looks like. By their estimate they have the number of devs required, therefore to them it must be the devs

Management does not understand what a "3-4" workload looks like. By their estimate they have the number of devs required, therefore to them it must be the devs that are the problem, not the number of them. It's not as simple as getting more devs, it's justifying another half mil a year in wage costs for that team. The people at the top with the pocket books really don't like that. Is your manager going to risk their neck, bonus, review? No. If the dev doing all the work burns out thats not seen as a fault of management by other management. That dev likely did that work because they don't understand the politics and had a mortgage and a kid in school to pay for. They want to be able to claim their work for the next job interview/resume. "I did less work while the project failed because bad management." is not a selling point.