The moon is in practical terms infinitely far away, and no matter how far the insect flies it won't budge and stay as a stationary feature to localize by.
But do the same with a lamp that's only 3 m away, and keeping it in the same spot can only mean flying around it in circles, towards, or away from it, otherwise it'll move around a lot relative to the insect observer.
The spiraling in might also be a kind of vertigo response as well. Normally the moon only goes up or down in your field of vision if you’re adjusting your angle - pitching or rolling. But an artificial light source moves up or downwards if you’re changing altitude but maintaining attitude. That would make flying up past the light ‘feel like’ pitching away from it, which might cause autonomic steering responses, similar to inner ear/visual conflicts causing humans to stagger and fall over.
The moon is in practical terms infinitely far away, and no matter how far the insect flies it won't budge and stay as a stationary feature to localize by.
But do the same with a lamp that's only 3 m away, and keeping it in the same spot can only mean flying around it in circles, towards, or away from it, otherwise it'll move around a lot relative to the insect observer.