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

@wlutke 
its been maybe a year since I have lubricated the main bearing, but when I did, I didn't notice any change.  However, thank you for reminding me that it's time to do that again.
Also, isn't acoustic feedback the same as rumble.  If not, what's the difference?
@dwette 
a rumble filter may be a band aide, however, when engaged, I notice no loss of anything (transparency, detail, staging, etc) other than the pumping of my woofers.
@nrenter 
ok, so in the purist form, inserting a filter in the circuit may not be 100% kosher, however, if your traveling down that avenue, why do designers use crossovers in their speakers rather then design them cross-overless, why use a speaker cable with connectors on each end (rather then use bare wire, and solder it directly to the amp/speaker), why do designers of electronics use IEC connectors for the power cable, rather then hard wiring it (as some do) on and on.  These all affect 'ultimate' transparency, and are design choices.  I just don't believe that any of the things you mention can't be done with no loss of performance, or ultimate cost (1-another switch in this signal path....how many switches/connections  are already in the signal path, are you saying one more switch is going to degrade the sonics to the point where it's so audible that it is going to degrade the sound of your system to a point of dissatisfaction?      2-, after all, in a phono preamp costing several or more thousand dollars, how much more can a 'high-quality capicator' add to the final cost of a product? 3-a change in the circuit design...ok...I agree with that.  I am not trying to be combative with what you are saying, I just believe that these items that you mention can be dealt with in an effective manner.  Happy New Year!

There are just too many factors that create rumble or acoustic feedback (still don't understand the difference), and there are too many people that experience this problem.  I use my KAB rumble filter, with no loss of sonics, so I want a phono preamp with this included.  The only negative I have with the KAB is that another set of interconnects is needed.

@louisl 
I guess it depends on the system, but when I engaged my KAB RF-1 – whether in a tape loop or inline between phono and pre – I experienced a loss of SQ. That is why I made the effort to fix the root cause of the problem, rather than patch it with a kludge.

Louis, with whom are you arguing? None of us is against the idea. Many older phono stage designs, especially from japan, DID incorporate a rumble filter. So if you really want that feature, find one of those.  American products from around the 1970s maybe up to the 1990s also can have rumble filters built-in. The lack of a rumble filter on modern phono stages is partly a symptom of laziness among manufacturers, and their desire to cut costs while also raising prices. And finally, the outboard KAB filter is really no different from what you would get if it were built into a phono stage. So, you can add that function to any phono stage, via the KAB filter which you apparently already own. But first of all, I think it is important for you to figure out the source of the rumble. Rumble is just another word for low frequency noises. There are many causes. Sometimes the problem can be cured without resorting to a filter. For example, is your cartridge well matched to your tonearm? Perhaps the resonant frequency of the tonearm cartridge combination is too low, causing the system to resonate due to foot falls or subtle record warps.

By the way, if you don’t like the idea of an extra pair of ICs in order to incorporate the KAB filter, you could hard solder the device in-line with your preferred phono ICs. That would satisfy even a purit zealot.

@lewm 
sorry, don't mean to sound as if I'm arguing.  It's a New Year, and I have too much to be thankful for!
My TT is very well isolated.  I can literally do jumping jacks directly in front of my TT, without affecting the tonearm while it is playing a record.  So, no problem with foot falls.  I believe the problem is acoustic feedback (volume low....... no rumble, turn the volume up....rumble).
You bring up a great point about the matching of my Cartridge and tonearm.  I will check on this!  That may be the problem.  Thanks for that suggestion!
Bottom line, like you,  I would like to identify the source of the rumble, and correct it, rather then use the KAB filter (however, I really hear no drawbacks when using it).
Hope your having a Happy New Year, and again thanks for your input!