There are none so blind as cannot see.
For those of you who reckon there is "nothing to see" here or that this issue is a mere administrative nicety, I suggest you look at the Merchant Navy( from whence the practice and nomenclature originate )
In the 60's the world fleet was dominated by British and Northern European flagged ships . I'll use the British fleet as an example but you could substitute any of the traditional maritime states.
Ship's officers were well respected in society and a Captain or Chief Engineer was a position of prestige and reward.
Cunard,P & O, Union Castle, Blue Flue, Bank Line,Blue Star,Furness Withy, Port Line, Clan Line, Ben Line, and a multitude of others were household names and dominated world trade.
All the senior officers were British , as were most of the ratings and lower ranks.
The passenger trades were crewed by british stewards and catering staff from top to bottom with a few exceptions.
Companies had in house indentured cadetship schemes to ensure a supply of highly trained and qualified personnel rising up the ranks.
Fast forward 50 odd years.
Virtually no international trade is carried on British ships and a British Captain or senior officer is rarer than hen's teeth. There are no british ratings to be found even on the home trades. Your ferry from Dover to Calais is likely to be registered in the Bahamas,have a Polish skipper and Filipino crew. The Red Ensign has re-emerged after virtual extinction but is itself now a "Flag of convenience" . That huge container ship you saw sailing up the Solent with the London registration is unlikely to have a single Brit or commonwealth person on board. Supply boats based in Aberdeen are manned by Eastern European officers and third world crews. They trade exclusively within UK waters.
Fast forward 20 odd years.
Heathrow is lined with wide body jets on Irish,Icelandic,Lithuanian, Panamanian or Timbuctoo registrations. The flight crew are from Eastern Europe or the Far East. The cabin crew are Filipinos on three year contracts who stay in a large dorm in Slough, work to Panamanian FTL's and get paid 30% what a british hostie would accept. They operate LHR-JFK-LHR then have a day off. The Brit hostie is extinct.
Your holiday jet to the sun will be similarly operated but from a point even further down the food chain.
The regionals will be crewed by P2F Ukrainians trying to get onto the job ladder or rejects from the "New Majors"
A few older Brit management pilots will hold key posts in offices and provide cast iron procedures and processes for their cheap third world crews to follow. They themselves will eventually die off as nobody will be rising through the ranks to replace them.
It's coming folks!