It's the oposite, trying to route or switch on variable length prefixes(as you would with IPv4 or V6), is pretty horrible to do in hardware, thanks to CAM it's

It's the oposite, trying to route or switch on variable length prefixes(as you would with IPv4 or V6), is pretty horrible to do in hardware, thanks to CAM it's atleast doeable. Route or switch directly on MAC addresses is ok, but creating policies becomes painful as there's no hierarchy. With MPLS, you get simple fixed length headers with single integer values is quite easy to push/pop and look up in hardware, and you can have software to generate the policies and manage hierarchies, placing the complexities and hard work at the MPLS edges, and having simple/dumb (aka. cheap) devices in the core.