Although I don't care much for the pairing one pro about it could be that out of numerous couple they have been somewhat iconic.
Part of it could be the imagery borrowed from Eros and Psyche personifying an aspect of love from Roman Mythology.
There was also the fact that X-men was quite popular back in the 90's and due to it being an introduction for many Psylocke and Warren may be nostalgia googles for some.
The fact that it was brought back in remenders UXF run could be seen as that but then again he brought a lot of 90's themes in his book with a modern twist.
That is all I can honestly think about really since I believe it had a nice run but after that I don't mind them seeing other people.
For the imagery this is what I mean