Lets take for example the US, with a large number of carriers covering international routes with types that are also in use with carriers in low living wage countries, an airline as an employer has the capability of employing someone suitably rated and with time on type that enables the capacity for a lower cost pilot that has the requisite experience. the long short can invariably lead to a stagnation level for career development for US citizen pilots, who will be left picking up the jobs on regional and internal lo-co carriers, while the long term career prospect, the long haul and heavy aircraft flying on routes that can be crewed by destination locals.
you must have US citizenship or a green card to work for a US company, so hiring destination locals doesn't work.