ShepherdsDog ShepherdsDog:
It should be determined if this is a natural progression or if there has been some other environmental influence, such as pesticides.
Or changes to temperature...
$1:
Some skinks, they argue, simply retain the egg in the uterus for a longer period of time to protect it from colder external temperatures. The longer the egg is kept in the uterus, the thinner the shell becomes. When a skink is born live, all that remains of the shell is a thin membrane, which the mother helps the baby break open.
The cold explanation cites a 1996 study and explains why the mountainous skinks are making the leap to live-birth faster than their lowland counterparts.
The young may be born "live" but there is still a membrane remaining, just not a hard shell, like with an actual egg. I see it more as an adaptation to the external environment the lizard lives in. I am uncertain as to the changes this region may have experienced temperature-wise over the years. Perhaps this would offer an explanation.