Because they're not: the distinction between "Religious Taoism" and "Philosophical Taoism" is generally recognized as an Orientalist[0] conception i.e. an excuse to talk about the parts they liked or could think of as Western (Philosophical) and ignore the parts they didn't like or couldn't (Religious). It's viewed as emerging from a collection of oral master-student based traditions that have always included spiritual components, such astral-project/"far walking" and mystic unity with the Dao. There wasn't a distrinction between philosophy and religion like there is today, hence why a lot of Chinese philosophy relies on concepts like Tien ("heaven", though more in a process sense) even if it seems otherwise secular/philosophical.

[0] I think you still see this mix-up today due to a lot of people reading the TTC or the Zhuangzi from Gutenberg or some other free online translation, not realizing that all those translations are from the 1800s and not a reflection of modern scholarship. For example, Laozi hasn't been considered a historical figure for a while now.