I think Horford is just not very desirable. There's a difference between "limited" player and "guy who is paid like an all-star who might be on your bench." And the salaries still won't match exactly.
Obviously all these blogs and speculative stories are meaningless, but most of the mainstream journalists still think you only move either player with a big sweetener (either a first-rounder or Thybulle, Smith if they are lucky).
Here's one trade proposal from Bleacher Report:
Philadelphia 76ers receive: Buddy Hield
Sacramento Kings receive: Al Horford, No. 34 pick (via Atlanta Hawks), No. 36 pick (via New York Knicks)
And here's a fan proposal on Reddit that I wouldn't do in a million years (though apparently it originally did not include the Sixers pick and people thought the Kings were giving up too much).
Sixers receive Buddy Hield, Nemanja Bjelica, 35th pick in 2020 draft, Sacramento 2nd in 2021 draft
Kings receive Al Horford, Matisse Thybulle and 21st pick in 2020 draft