Why don't you try the dental band mod if you want silence?
Good question. Many reasons, some of which may not be good reasons. They include: 1) I've read it slightly shortens the keytravel, which would bother me, 2) it costs money, 3) having experienced the type-s switches from both PFU and RF, I feel they work great and retain a great feel, 4) I'm lazy and right now am resisting seeking out the dental bands online, purchasing them, then taking the time to install them, etc. Like I said, not really good reasons but it is what it is.
Also, lately I am leaning toward not buying the silenced 55g RF 87U I've seen online and waiting until I can find an ANSI all-45g silenced RF 104. I am sort of fickle when it comes to full-size vs TKL or 65% types - I keep changing my mind as to what's best for me.