Have you not seen how big number can be? Number can just get so big. I don't even care that I'm ADHD and I'm playing into all the worst stereotypes about us:
I couldn't say why it got me so hooked. I like roguelikes/rogue-lites as well as deckbuilders, and I think it hits a really good balance of the things that make them fun - challenge, randomness, a variety of strategies that can make different runs feel very different. Also good achievements and unlockables.