Do you have the internet? Are you aware of news resources?
The question to 'why' is simple: it was a deliberate strategy. It's precisely what they planned on because of benefits.
https://www.cbc.ca/news/health/covid-19-pfizer-second-dose-delay-more-antibodies-study-1.6026765
In short: first shot of the vaccine has more effectiveness than originally thought (trials were quite limited and done on the three-week recommended interval, so there was no certainty that waiting longer between shots would be better, although they had good reasons to think it would work better).
Decision was that it would be a better strategy long-term to give first shot to as many people as possible before prioritizing the second shot. (In part because one shot seems to have a strong effect in reducing severity, and reduced severity means less hospitalizations and the negative impacts of having health system overloaded).
You can disagree with the recommendation or the science behind it - it was a relatively risky decision at the time it was made because the information wasn't clear at the time; subsequent studies have
mostly shown it was the right decision. (Although criticisms possible too - for some sub-groups like elderly may be better to priortize second shot).
And there's good reason to criticize about slowness of rollout and delivery, although since about mid-April, deliveries and vaccinations have really accelerated. (BTW those estimates of when Canada will switch to second doses - likely to be moved up to before September as deliveries continue to be very high in June and going into July; so for once they're likely to beat the targets, if no major hiccoughs).
Meantime: go ahead and compare the numbers now for France and Canada. Canada: more total doses delivered, more in % of pop that have received one dose (dramatically more, like 20% delta, 38% to 58%), and France - about 10% more of pop that has been fully vaccinated (16% to 6%). That's hardly stellar, with a likely irrelevant benefit from group/herd immunity between 16% and 6%. About the only benefit it would have - seemingly - is making individuals feel better about scheduling their second short earlier.
https://www.cbc.ca/news/canada/track-how-many-people-have-been-given-the-covid-19-vaccine-across-canada-1.5870573
But if you're asking why and wondering if it's because 'poor', well, try the internet, boomer.