Possibly RBC is just more generous than AMEX is, from RBC's POV their Avion product is very strong as it is and with their cards being VISA they are accepted everywhere and people are more than happy to take on the Avion cards without transfer bonuses (most people don't even use them). Where as AMEX is less accepted in Canada and is harder to rack up points, which means it makes more sense for AMEX to have more transfer bonuses so people feel like they're getting more value. It's also another reason why AMEX has a declining market share in Canada, many people don't carry an AMEX because its just a waste of space in their wallet amongst other cards.