People who still hold SBD is only for speculative reasons, hoping it will one day go back to 1 USD

There have always been people holding SBD, even when it was $1.

You seem to deny that people value stability of value, which absurd.

just go back to STEEM whitepaper written by Dan Larimer.

SBD isn't supposed to be pegged to 1 USD. 1 SDB is designed to try to have the closest value of 1 USD worth of STEEM.

I'm not even sure what that means, but on page 5 of the white paper I see this:

The Steem community provides the following services to its members:
...
"3. A stable cryptocurrency pegged to the U.S. dollar."

why not focus the discussion/work how to make SBD actually useful?

That's what this is all about. Making it (more) useful by making its value (more) stable.