Most likely as a concession to getting Quebec to join the country
Same reason why we have things like the notwithstanding clause that allows provinces to overrule the constitution
You meant not leave the country, Québec, Ontario, Nova Scotia, and New Brunswick are the founding provinces and Québec had almost no leverage at the time.
Quebec was controlled politically and economically by english speakers when Canada was formed. The decentralized political nature was more practical due to Canada's sparse population at the time. It's a blessing and a curse.