Why?
The purchase of interim Super Hornets from Boeing is stalled, if not dead in the water. That is the result of Boeing’s decision to go after Bombardier on its C-Series commercial aircraft and the resulting duties from the U.S. of almost 300 per cent.
The potential acquisition of fighter aircraft from Australia is a possibility. But that won’t happen overnight. Australia will respond by the end of December but that is just the beginning of the process, if it does proceed.
The CF-18s will be upgraded to allow them to keep flying to at least 2025.
But even Defence Minister Harjit Sajjan has acknowledged in the past that the planes could remain in the air much longer. In November 2016 on CBC Radio’s As It Happens, Sajjan said the jets might be required to keep flying until 2032. (And that was before the issues emerged with the purchase of interim Super Hornets from Boeing).
This is all despite the fact that DND stated, "An ELE extension to 2030 is assessed as a high risk option in terms of cost, schedule and technical factors" in its now Archived CF-18 Hornet Estimated Life Expectancy document.