Did Promaster quit "making" lenses
Promaster never made any of their own lenses (as far as I could determine).
What they did do, was rebadge 3rd party lenses (usually Tokina or Tamron) as "Promaster". The big diffrence was that Promaster offered a lifetime lens warranty :
"Photographic Research Organization Inc. (PROMASTER) warrants that your PROMASTER Spectrum 7 Lens, purchased AFTER 1/1/2000, will be free from defects in materials and workmanship for as long as the product is owned by the original purchaser."
Warranties are only as good as the guarantor. Perhaps too many people cashed in on their "lifetime" warranty and Promaster went bankrupt. Or...declared bankruptcy while they still had some money left to enjoy life.
The Five 'Ps' of Photography:
Proper Planning Prevents Poor Performance!