I've flown BRU-SOU in a Loganair Jetstream many years ago!
However most of the recent posts about this route refer to the good old days before Eurostar services to Brussels came down to only 1hr 50m - right to the centre of Brussels, not to Zaventam out on the outskirts.
Maybe many ex-pax from the catchment area north of SOU now find it quicker and easier to go by train.
In recent years Eurostar has absolutely hammered Paris and Brussels air traffic.