The motivation is obvious: people want hard money, and some economists wish they didn't. So they deny the obvious: inflation is a punative tax on savings and make up b.s. psych nonsense.
They're perfectly smart people, but not ethical enough to tell the truth.
We can hard fork in inflation later if it's really necessary. For now better to socially have BTC be stable.
I can think of two reasons, one relatively straightforward and one subtle. Hint: my last scaling bitcoin talk.