Summer is historically a slow time for pinball sales. I wouldn't read too much into it.
As for those STTNG; maybe they just weren't priced correctly. Maybe that title isn't in particularly high demand at the moment... Who knows?
Things will always fluctuate.
I'm at a stage where I don't really want to invest more money into this hobby and am starting to downsize a bit.
But, there are always new guys coming in... looking to build up a collection.
Until the current generation of 30-50yr olds is done collecting, there will be a market.
I'm actually hoping that, when I turn 60, I'll be able to buy a TZ for what it costs me to buy an EM today