That does raise the question of what those tech companies' motivation really are though.

The processes you described would work really well if the goal is to meet a hiring target and ship just enough product that marketing and sales can run with it.

If they don't necessarily care about quality of end product or quality of the engineering that went into, throwing heavy process at the team may get them there just fine. That heavy process may even work better for them if the goal is more managerial control to meet sales and marketing deadlines.