They are a strange mix - I understand Arsenal v United, it's the stand out tie of the round, these are BBC's only live matches so they want some audience share and that will have an audience. Accrington, Millwall, Barnet are all potential giant killings so good exposure for those clubs and some neutral interest (and Barnet v Brentford causes less disruption to midweek tv schedules) - but Palace v Tottenham & Chelsea v Sheffield or Luton? not interested - perhaps local derby interest for Palace - but what about Shrewsbury or Stoke v Wolves - local derby and lower league v Prem. or follow Oldham or Newport after their exploits of the last round.
I wouldn't expect our game to be picked - for the above reasons - other than a chance for BBC to show the Champions live, which they don't get very often or because it's more interesting than Chelsea at home to a lower league team.