When Nevada casinos began in ernest to not honor their chips for redemption.
When Nevada Gaming took on an anti-chip collector policy and began not to approve chips relating to meetings, conferences, conventions, holidays, etc.
When boxes of previously scarce to rare chips began showing up in the marketplace.
When the Playboy hoard was unearthed in Mississippi causing the value of previously valuable chips to collapse.
When casinos in Atlantic City stopped issuing LE chips, many collectors lost interest
when they could not add new chips regularly to their collections.
When gaming tokens were replaced with TITO.
When silver strike machines were withdrawn from casinos in A.C. and Nevada due to the escalating price of silver.

Just a few benchmarks in my opinion... there are many other examples, but then, what do I know...?