Well, that's just how I tailor my cards to work for me. If you spend your hard-earned money on your cards it's better to make the most out of it right
But I also like assigning personality for my decks. I feel as if each deck has a different view toward certain things. 4 of Pentacles in RWS is a man holding tightly onto his coins, indicating selfishness. But 4 of Disks is Sun in Cap in Thoth, suggesting determination toward goals. It's like asking two people about the same thing and hearing different viewpoint. You just have to choose which person to give you the best advice in which situation. So getting to know my decks' personality can really enhance my reading's accuracy.
And yeah, like Astrology, I find myself using a lot of psychology with Tarot and Lenormand. Really, if you don't have any knowledge of psychology how can you understanding the different meanings of the cards and convey your understanding to the querent? There is always going to be contradicting things during your reading and you have to know how to make sense of them. And isn't your querent here to gain a deeper understanding of their situation too?