Chuck wrote:

Why so?
I find it very useful and practical when it is available.

Boy, the installer for the mode S a year and a half ago didn't mention
that it was either impractical or obsolete!

It is impractical from a total systems perspective. It's not unlike TLS
and ILS.

I am sure it is a nice-to-have when you're in the limited service areas.
TCAS, on the other hand, works everywhere independently of the FAA's ATC
system.

It's a niche solution and competes for resources.