repositories very out-of-date for Thunderbird version?

[home user]

I very recently asked a question in the Thunderbird support forum. One 
person replied
"Find yourself an updated Thunderbird...".
I have version 60.7.0; the person implied that the current version is 
68.  That's 8 versions out-of-date.  I do a "dnf upgrade" every Thursday.

I did a "dnf check-update thunderbird" this afternoon..  No new versions 
are available.  Why are the repositories so far behind on Thunderbird?

thanks,
Bill.