>> As far as I know chkconfig was never a Debian tool. I only know it
>> from RPM distros. Maybe someone tried to include chkconfig in Debian,
>> but gave up later. Or it never really worked.
I frequently used (and liked) chkconfig because it did work well on Red
Hat Distros. I can see that Debian would be an issue as the init scripts
use the LSB format which Red Hat did not. Red Hat's scripts execute in
the order they list in.

https://wiki.debian.org/LSBInitScripts

'Required' vs 'Should' vs 'Default' vs 'X-Start-Before' vx
'X-Interactive' need to be compared against each other in some sensible
and predictably consistent manner, it just didn't work.

I frequently came across issues with LSB format init script unreliable
reordering whenever a service is added or deleted, causing services to
fail at boot or change of runlevel.