Fixed inflation formulas in crypto projects have always annoyed me. It's a recipe for disaster because you basically have to have economic growth that matches the rate of inflation just to stay even (not quite, but ok for this discussion). Most real-world currencies have some means to influence inflation when they need too.
I guess it comes down to what you want to control; exchange value is a pretty important metric in crypto. Most central-bank based economies use inflation manipulation to control their economy and exchange value (with other fiats) is a concern but often not the primary concern. I think exchange value matters so much in crypto because most tokens quite simply do not have a vibrant internal value transfers.