GMT is not at all exceptional in the relevant respect, of referring to
a specific offset rather than to a civil timezone.  MST (aside from a
Moscow-based interpretation) refers specifically to UT-7h, not to the
dance that clocks perform in Denver.  Likewise, MDT refers specifically
to UT-6h.

To accurately represent GMT and BST (as used in the UK) and MST and
MDT (as used in north America) in the timezone database, you'd need
essentially:

Zone    GMT               0:00  -       GMT
Zone    BST               1:00  -       BST
Zone    MST              -7:00  -       MST
Zone    MDT              -6:00  -       MDT

and similarly for rather a lot of the other abbreviations.  (It so happens
that two of these four hypothetical zones are already in the database
(GMT and MST), but that's unusual among the abbreviations.)

If you don't do this, but instead have just links such as BST ->
Europe/London, then at best it's still necessary to search within
the timezone data to find out what the abbreviation means.  That's
not actually representing the abbreviation's meaning; it's a bad
implementation of the hypothetical abbreviation-to-candidate-zone
index.  (Bad largely because it can only show one candidate zone per
abbreviation.)