Sintering plastic is a more complex way to produce UHMWPE. Extrusion is an easier way, so it's cheaper. Not sure which way came about first. The thing is we all know that sintering the plastic can produce amorphous regions where the wax molecules can reside. It may be that it was not planed that way, I really don't know.
Crown invented a new way to create a sintered base plastic that is unlike the others, thus there base plastic is cheaper to produce. Total trivia.
Sintering is not a complex way to produce UHMWPE. The UHMWPE is already produced - in very long chain lengths.
In this case, it is a way of taking little beads of UHMWPE and quasi-melting them together. Under very high pressure to boot,
We do not all know about those amorphous regions. It is still not clear to me how meaningful amounts of wax would penetrate and reside on the base material.