Cause its WAAAAAY more easier to just spend less than an hour to lift the cab and have full access around the engine. Have you ever removed the grill or the bumper and the entire frontend? All those bolts you gotta keep track of. Lifting the cab, its 4 bolts and unplugging come connectors..thats it...i had access to a lift which made it easy for that...guess i should've stipulated that.
But If you're a contorsionist and have small and skinny arms...have at it with the engine in there

But like I said, its a time for upgrades....ie, grid heater delete...headstuds...and checking on potential probs while you have full uninhibited access all the way around the engine