I'm not sure what you mean by that, there are new & improved models of 3d printers coming out all the time and decent hobbyist printers are becoming available for progressively lower prices.
I believe the major fdm patents were filed decades ago and little was done until recently when they expired.
Parent is probably talking about SLS (selective laser sintering). Patents expired in 2014.
Yes, that started to happen once the key patents expired.