On the other hand, I could imagine in theory how they could be differentiated (namely one doesn't necessarily have to explicitly reference the geometry of projective space at all times while studying it).
On a third hand, people might not be likely to obey such a distinction in practice, and questions concerning the geometry of projective spaces might predominate over questions concerning other aspects of them (I don't know if this is true or not).
And on a fourth hand, perhaps it might be useful to have the two tags merged so there is a larger community surrounding them. Or maybe it might not be useful for literally the exact same reason (e.g. the people studying the geometry of projective spaces could drown out those studying their other aspects).
An example of when people seem to benefit from having similar tags being separated is "probability" and "probability-theory", for example, so this might also be the situation here -- in any case, it is not clear to me what the etiquette surrounding these two projective tags is from their tag descriptions, which is why I wanted to bring it to your attention.
Anyway, I am not sure if this is something which other people have noticed before, so perhaps anyone who is an expert in either of these areas (I am not an expert in either of them) would be interested to know that both these two very similar tags exist. Again, I am not sure of anything.