Why does dig +trace ignore Additional Records?

[Garri Djavadyan]

Hello list,

I am also interested in understanding the reasons behind this
behaviour, especially after reading the following snippet from the
official knowledge base [1]:

   When following delegation iteratively as specified with the +trace
   option, dig will begin by requesting the NS records for the servers
   authoritative for root (".").  These may or may not be supplied with
   glue - that is A and AAAA records that can be used for the next
   queries dig has to send.  When there is no glue provided, either on
   the initial query for the root nameservers, or later on when
   following delegation, dig will revert to recursively querying the
   servers listed in /etc/resolv.conf to obtain the needed A/AAAA
   RRsets.

Many thanks in advance!

Garri

[1] https://kb.isc.org/docs/aa-00208