look you
I think you'll find that Swiss, Austrian, Brussels Airlines, Lufthansa (and, until recently Blue1) have all purchased or leased slots from BMI...presumably they have all absorbed as much of the BMI LHR slot portfolio that that reasonably can at this stage so BMI has no choice other than to look elsewhere for sales.
I would guess..
(a) these 6 sets are slots for operations BMI really cannot afford to carry this winter on daft extra LHR-MAN operations or whatever
and/or
(b) DLH is getting to the end of its tether in pumping cash into BMI so the BD management are under much more pressure than hitherto to raise cash themselves for the immediate interim until the long-term future is decided