It's simply how the higher end aircraft leasing business works. You'll find a majority of those aircraft registered in Bermuda are owned by lease companies in Ireland. There are various reasons for this from tax structures, registration laws, asset protection issues, etc. Its been this way for some time with different host countries at times..
But the AWC is how you prove to other countries that that your aircraft does meet a minimum standard per the Chicago Convention/ICAO. You'll find the vast majority of any ICAO country's civil aviation rules and laws (to include the FARs) are to meet these international conventions. Without them you can't move aviation assets outside the host country like Canadian owner-maintained aircraft and now any Russian operated aircraft top any of the other 180+ ICAO countries.