Because they can stay in Europe, but not really.
Turkish teams can participate in European cups, so the players who play at Turkish teams stay relevant. For instance, next year you won’t be wondering where Mario Gomez is, because he’ll be playing in Champions League.
In recent years, players who are transferred to Turkish teams can find their way back to other European leagues too, hence still staying relevant in the European football.
Turkish league is a competitive one, it’s an exciting one. But as a football player, you do not have to be on your top shape to play well. Players don’t have to be fully fit to play good. If you take an average team from Premier League and put them in Turkish league, they will perform better just because they are fitter than Turkish teams.