It certainly is a shame - Perhaps he should have raised his fee, but I suppose the actors can’t be blamed. In all but the case of so called ‘Superstars’, when actors are offered work, they take it … and Van Cleef probably knew that it’s better to work in low budget stuff than not at all.
I also think it’s a great pity that he didn’t get a better deal in America - but by the time he appeared in ‘Escape from New York’ (1981) he looked really old, though he was actually only about 55 
I actually don’t mind his 1971 films - ‘Captain Apache’ (Rubbish, but fun) ‘Bad Man’s River’ (Has some genuinely funny moments, though overall it’s not great) ‘Return of Sabata’ (disappointing, but the good outweighs the bad)