I see a whole load of unwanted Js, Qs, Xs, Ys and Zs in Europe, too...
ABZ (Aberdeen Dyce), BHX (Birmingham International), TXL (Berlin Tegel), SXF (Berlin Schönefeld), SXB (Strasbourg Entzheim), HUY (Humberside), BLQ (Bologna), LYX (Lydd), MXP (Milan Malpensa), HAJ (Hannover), LEJ (Leipzig-Halle), BIQ (Biarritz), Groningen (GRQ), Bergamo (BGY)...
I can only assume these are 'filler' letters when other combinations of letters are unavailable.
And of course, the 'can't find a relation' ones:
MME (Teesside Middleton), AGP (Malaga), ACE (Lanzarote), St Etienne (EBU)...
Historic reasons?
Then there are those with unobvious 'extended' airport names:
NWI (Norwich International), CWL (Cardiff Wales), LYS (Lyon St Exupéry), LBA (Leeds Bradford Airport), MJV (Murcia San Javier)...
But then, you seem to have some country-specific fillers. Like in France:
PUF (Pau Pyrénées), CCF (Carcassonne), CMF (Chambéry), PGF (Perpignan), TUF (Tours).
(Or in Canada, as previously mentioned).
Dunno, really. I guess it's all down to who gets there first...