Note that striker was post-81, and the rules for personal scale vs ships in s7 make bk4 weapons, even the rpz, pretty useless at ship scale.For point defence in space combat the argument would be that they lack range. For use on the ground, B4 didn't have any rules for spaceships, HG was about major ships having it out in deep space, and Striker could've had such rules, but presumably Frank thought them a poor use of word count - not really on topic, and if someone wanted to add a small gun to a space ship they could whip up some rules easily enough - at the time of publication (1981) people doing that was the norm, after all.