The fans expect too much.
These days, most international teams are nowhere nearly as good as (let alone as well resourced, or well trained) as the best of the national teams in the best of the respective domestic leagues.
Above all, the very best of the domestic teams play to a system - a well-drilled, well-oiled, well trained - system, -
which is manifestly not the case with international football, where there is neither the time nor the bottomless resources to train individuals to play to any such system.
Moreover, an international manager can expect to receive (or choose, or select) players from a number of teams, teams that are playing a number of different systems where the players are well used to playing with one another; with time pressure (and demands from entitled and intolerant fans) he is still required to somehow craft, or create, a functioning and coherent team from several disparate (and not always equally talented or gifted) individuals.
Thus, - unlike in the past - international teams tend to play at a less sophisticated (and less regimented) level than do the best of the domestic club teams.
Given the resources (not least, the actual individual players) at his disposal, I think that Southgate has done brilliantly since his appointment as manager; his teams have reached the finals (not just the semi-finals, which would be an already exceptionally impressive achievement) of two international tournaments, and done so in the complete absence of scandal, idiocy or controversy on the part of the team or officials.