If they bother to actually read the basic guide, it's clearly stated:
https://www.canada.ca/en/immigratio...application-sponsor-parents-grandparents.html
Do I have to maintain a minimum income during the processing of the application?
Your Minimum Necessary Income must meet or exceed the Federal Income Table for Parents and Grandparents Sponsorship above on the date on which the sponsorship application is signed until the day your family members are granted status as permanent residents.
Income may be reassessed at any time during processing if new information indicates that you may no longer meet the minimum income requirements or if more than 12 months have passed between the dates on which we receive your application and when processing of the application begins.
It's also plainly obvious that the income table goes up a little bit every year, as the 3-years table is literally right above this statement in the guide.
The whole point of 3-years LICO is to see
consistency, that the income you're showing will be maintained indefinitely going forward. So people with sporadic income up and down that can't get 3 consecutive years, can't sponsor parents since there is a higher chance they will be unable to support them in later years.