RPGMemes

It doesn’t explicitly say they can only siphon from others.

And it doesn't explicitly say they cannot fly yet no sane person would infer that this spell makes you capable of flying. The spell does only what it says it does, otherwise you are still bound by all the base rules and limitations of the game, like not being able to willy-nilly siphon life force out of things without a feature that explicitly says you can.