As far as I know, this kind of "slide helper" was already usual in the Renaissance.
Have not seen those much in our times to be honest. Anyway, might be
of great help.
Back to topic:
One could as well ask the question:
Why the cornet for any comeback player, amateur, professional,
brass band fan, jazz musician etc.?
It is as simple as that: It is a great instrument with a unique tone and a long history, and fun to play!