The rest of Canada and other countries got better coaching/preparation programs for young players and caught up over time while Québec coaches did not really change their methods as much (luxuriated in past successes and old-timer approaches actually) from the late 1980s until the mid-2000s. And we're still lagging behind while others are continuously improving, hence why there is less talent developed compared to the past.
Historically speaking, at the same time as the overall level of coaching stagnated/declined, the province experienced a major downturn in interest for Hockey (given how expensive it became to play, plus other sports becoming more attractive, like Soccer) which, compounded with other facts like Hockey becoming a more global sport, explains why we don't see many young Québec-born goalies make it to the NHL.
In fact, given that Russia's development system for goalies has become the world's best in the last couple of years/decades (they put a great emphasis on it since the days of Khabibulin being their only good goalie), I expect yet more russian netminders to make their way into the NHL and thrive there before another country implements a more effective development system and takes over for a little while as producer of the best goalies.
And I don't expect that the top of the charts for goalie development will ever belong to Québec again, unless yet more truly major changes happen across all levels of youth hockey in the province.