The problem seems to arise when a club doesn't have a clear idea what it wants to do or what sort of club it should be. Different types of clubs serve different purposes, and it doesn't do to mix them up.

If a club runs as a singaround, or with only local amateur guests, it will raise expectations among would-be performers that they will get to sing, and among audiences that the entrance fee will be low. It is then unsurprising that they are reluctant to pay more for an occasional professional guest - neither the higher entrance fee or the professional performance are what they want from that particular club. For a club of this nature the occasional professional guest night perhaps isn't appropriate - it may be better to put that on as an entirely separate one-off concert, possibly at a different venue and on a different night, rather than as something which doesn't fit in with the club's usual style.

The sort of club which Musket describes and which used to be commonplace, if not the default, encouraged high standards from both guests and floor singers. However there was a financial risk which I guess fewer organisers are willing to take on. Nevertheless I sense that the remaining clubs still using this format are doing well.