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


In my system, the use of a rumble filter is mandatory (I notice no degradation of sonics when I engage the rumble filter).  I'm thinking of upgrading my phono preamp and would like to choose one that has this as an optional feature.  However, it appears that most manufacturers of phono preamps do not include this.  Why not?  Does the use of a rumble filter degrade the sound of a phono preamp?
louisl
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. 
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.
@dwette...……………………

Agreed, but sometimes it is the ONLY option after all else fails.