Basically it's a developing country's problem.
Most of the people who were born before 1990's do not have birth certificate as mandatory thing as compared to many developed nations. So the 10th standard certificate/high school certificate is used as birth certificate proof. Also, there are many times some officials during your education or creating DL or creating other government cards, misspell your name or remove middle name or last name and you are OK with that some times.
As we never thought that we would be applying for Canadian PR, things work fine in the country we are born in. In case of any issue, Affidavit solves all the problem in our country.
So basically no mandatory birth certificate in our time is cause of the problem, but now days it is mandatory to have birth certificate and millennials will not face this issue.
Hope this clear your doubts