Alexander Hislop and his book 'The two Babylons' are quoted 47 times in the WT library. Hislops motive was to discredit the Catholics and mentioned numerous practices of theirs as being from pagan origin. He had his own set of weird and whacky ideas, which were not factual.
It would seem that the WTBTS in it's own motive of discrediting the Catholic religion picked up on this book and ran with his ideas. It fitted their needs of pointing at other religions and demonstrating that they were still pagan. Of course, that required ridding their own organization of those pagan practices that they they would choose to condem.
The WTBTS last quoted Hislop in 1985.
Hislop's writings have been discredited.
Hislop believed the Protestant religion was the true religion and he also believed in the Trinity. Having researched his writings the WTBTS would have known this. So why would they even quote someone whom, according to their own beliefs, was lying? Surely if the WTBTS has any credibility they would not quote from a person who's basic doctrines were a lie and from Satan, how could they even put trust in anything he was saying? Yet they continued to quote him time after time.