The SRT was scrapped because Toronto decided decades ago to just let it rot.
Remember, Vancouver had the same rolling stock and technology as the SRT and it certainly had problems at first but, unlike Toronto, Vancouver invested in the system and worked with Bombardier to produce better vehicles....................Vancouver had a lemon and made lemonade. Now SkyTrain is fast, reliable, comfortable, efficient, and frequent........the hallmarks of great transit.
As far cold weather/snow/ice being a problem, they certainly were for SkyTrain at first but again Vancouver improved the system with vehicles better designed to deal with it, heated the tracks, and when really snowy simply took one of the older SRT type vehicles and ran them all night with automation {which something Toronto also didn't do} and it keeps the tracks clear. We just got 27 cm of snow and hade temperatures hitting -14C and while there were a few glitches, in general the system just kept going reliably.