I think it's cultural. Managers today do daily stand-ups, one-on-ones, retrospectives, syncs, and all kinds of meetings. They are heavily invested in the day-to-day operations of the team. The societal expectation for this role is that they are hands-on, and when a problem arises, they will immediately do some shuffling or reshuffling to address whatever problem is at hand. In a sense, this is the outcome of agile-like methodologies spreading in the industry. If this is the tool we are teaching managers to use, of course it's the tool they are going to use.

I can believe it is deliberate at the top, I've certainly seen first hand in several orgs I've worked at.

My sense is that unless actively managed against, any org big enough to have a financial department and financial planning will work under assumption of fungibility.