It's not 'my' questionnaire, I'm just a TT user.
Since CRA doesn't have all your credit information, and may not have all necessary T-slips at the time you choose to do your tax return, then it is necessary to collect that information from the taxpayer. The questionnaire is simply a means of automating the process where a human tax preparer asks profiling questions.
The profiling step is intended to reduce the tax preparation time by preventing the user from seeing a large number of unneeded screens. Most all tax software uses this approach.
CRA puts the onus on the taxpayer to perform self-assessment in reporting income and credits, and advises you to check all AutoFill data for accuracy and completeness. This is good advice!
