When did LEGO stop producing Technic action figures?
The Technic minifigures last from 1986 to the year 2000. As far as I'm aware LEGO haven't released a statement on why the figures were removed. Minifigures are expensive and using them limits Technic sets to a certain scale. 

Having a dynamic sense of scale allowed Lego to create the £9.99 ($10.90) 8045 and the £61.65 ($89.99) 8295, two variations of the same model. One basic and affordable, the other focusing on realism.