Looks, simplicity, economics. Often people are missing parts, or the intake pipes are damaged. I'd suggest keeping the intake pipe and the crankcase vent if yours is in good shape. It simplifies everything and ensures the airflow into the carbs is no worse than the engineers at Yamaha designed it. You may need to fabricate a support for the filters, but that shouldn't be difficult.
My Maxim, being DOHC, never had the intake pipe that incorporates the crankcase vent. I'm keeping my eyes open for a decent example in the hopes of making it fit. I hate having the crankcase vent going to the air, and smelling the fumes.