I suspect that they have a quite substantial membership initially because it was "free", and are taking the pragmatic approach that they can retain and grow that membership if it remains "free to user" without allocating additional funds to support that free membership with physical things. Me, even though I've not actually purchased any of the range yet, would be severely tempted to take out a paid membership for the magazine and wotnot (club wagons would be nice...) but that's not to be (my loss).
The Hornby collector's club sent out wagons and locos for your membership, so this isn't an unknown to Hornby. Maybe a paid premium club membership might come down the line.
Whilst I'm not presently a member of either the Bachmann or Hornby Collectors Clubs, my impression was always that Hornby's "freebies" were more generous, but the Bachmann magazine was better for content. The TT magazines have somewhat redressed that in my mind.