The people who owned them, did not understand what it takes to breed monitors. One particular part is the social aspect.
Because their fine monitors are rare, they raised them up without other monitors. I am sure they did this to protect them.
The problem is, the experiences learned from being raised all by themselves, does not lend to becoming a good cage partner, muchless a good breeder. In fact, very much the opposite.
Its also possible, they made lots of other protective choices, that in fact hindered successful breeding.
The truth is, if they did not get offspring within the first year or two, the percentages of success drop quickly as the monitors become haggard(old and set in their ways)
I imagine, this goes for humans too. FR