Why don't all phono preamps include a rumble filter?

There is no reason to think about changing tables, I too have had three VPI tables never having a rumble issue with any of them, all supported by a lead balloon turntable stand so I started out with a good set up from the ongo. Symposium makes an insert to replace the rubber grommets that vpI uses in their feet that really work wonders for around $200.00. You should be able to get that rumble thing under control with very little effort.

Because 1) regardless if the filter was engaged or not, it’s another switch in the signal path, 2) if you’re gong to implement it with any transparency in mind, it’s going to require a high quality capacitor (expensive), adding cost to the product, and 3) may require a change (more complexity) the the circuit design. 

What I said.

louisl,
Have you inspected and lubricated the main bearing lately?  My HW-19 MK IV had no audible rumble at any volume.  The Technics in stock form may be more immune to feedback.  Could it be that you are referring to acoustic feedback as rumble?  As noted, there are solutions for that.

My personal experience is that a rumble filter is a band-aide (and a poor one at that) for not correcting isolation/vibration issues. I learned that the hard way and now have a KAB RF-1 Rumble Filter sitting unused (and unneeded) in my closet.