Grrr.
But ... A lot of people are not investment savvy, and freak out at the thought of anything they've put money into, going down in value. The thought of something ever losing (let's say) 1% in value compared to what they've put in, freaks them out even if it's something that can be expected to return (let's say) 5% on average if they ride out the peaks and valleys. GICs are low risk, but low reward. They are for those risk-averse people. And yes, the risk is that the guaranteed interest rate is less than the rate of inflation, in which case your investment withers away in real terms.
I am of the view that it's better to own the bank than to put money in the bank. There are good dividend-payers among the Canadian banks, and thanks to our regulatory environment, they are unlikely to go bankrupt any time soon. But ... they are represented by common shares, and those fluctuate up and down. Ignore that, and collect the dividends. (In your TFSA, to the extent possible.)