Space is vast. Like so big that you cant comprehend the distances involved. The stars we see in the night sky are very far away hence we dont have a revolving door of guest stars in our sight line. Think of it like this: if you see a mountain in the distance and you run 5 miles in any direction, the mountain doesnt appear to have moved at all, even though you know you moved 5 miles. As the distance between objects increases, the angle of the triangle formed from the observed object, your previous position, and the current position shrinks to imperceptible.

IIRC its not so much the rigid structure that determines the size of an insect but the fact that they rely on diffusion to oxygenate their cells. Get too big and the oxygen requirements of the creature grow too large to overcome without specialized organs like lungs.