Cost of cases, for starters. Cost of rifle, second. Availability of cases (.338 or .458 always available). Ease of building a custom rifle: any old Mauser 98 or standard-length Rem-chester is perfect.

Even recoil, when you get down to it! The Rigby needs significantly more powder than the Taylor for the same velocity.

On the Rigby's plus-side, much lower pressure. And plenty of room to juice it up, if you're one of those people who needs to do such things.....

Don't mistake my post for a dislike of the Rigby: I'd kill for an original John Rigby Magnum Mauser chambered for the cartridge!