Large expensive multi-ton CNC machines often claim raw weight is needed for vibration free cutting. While it is true that weight plays a central role in vibration control, vibration damping (like the shocks on a car) is an important factor as well. And remember increased weight means increased wear on components and a higher motor drive power needed.

A heavy machine will cost more to ship as well.

A well designed efficient lighter machine with the proper cutting bit is capable of quality cuts.

Also, remember that the router itself (which is quite capable of routing by itself!) weighs only about 20 lbs.