When I was there last year, there was only one staff member who appeared not to be a keeper(and they could have been one too), it's not like they have loads of catering staff etc and the talks/ tours were done by keepers.It is probably cheaper to run with no visitors and only keeping staff , rather than having a few visitors with all the additional staff costs involved with an open collection . Without external funding neither option is viable in the long term .
I wonder how much they spent on marketing the collection - if the general public do not know you are there they will not visit .
I don't think marketing has been great, though I think tourist information type leaflets were at the hotel I stayed at nearby and at Wingham, which I went to on the same day.
On that visit we arrived at 2pm and I think we were the only visitors that midweek October day. On my previous visit about 4 years before, there were only 4 other people there whilst I was and that was in late July!