I thought the work of Maria Reiche in linking the figures and runways with celestial constellations and the seasons was generally accepted as the most likely explanations for the glyphs.

The best theory I have ever heard, in terms of it being the most realistic scenario, is that the real reason was to keep a disciplined army busy between conflicts.

Under this idea, the occasional alignment to specific stars or celestial events is real, but not the real utility. The real utility is keeping a standing army ready during a period of empire building.

I always tend to favor historical hypotheses that use realpolitik.