Probably because parent is cherry-picking and has no source. The average flat in Paris is at €10k/m2, so 30m2 would be around €300k, not €1.2M.
It's amazingly cheap. Down from 3.5% ten years ago.
The downside of low rates is house prices correspondingly very high.
Repossession is especially difficult here, which raises the risk for the lender, and the banks unwisely gave out ECB trackers (as opposed to the EURIBOR trackers more common elsewhere) back in the day; some of these can be as low as 0.5%, so everyone else has to pay for that legacy.
Edit: put another way, if you pay 1k/mo on a 1.2mm loan, you'll finish making payments in 530 years. The Jeanne Calment loan!
Interest only loan will have lower monthly payments, but you will need to make an additional monthly contribution to an investment product, such as an endowment policy, in the hope that the investment product will be worth at least the outstanding capital at loan maturity.