Smite Item: Book of Thoth

Because other items provide high power without needing to be stacked (doom orb, tahuti), as well as building around (at least a bit) Thoth is ideal. Of course, if you're a mana hungry god you could just pick it up for mana, but generally you want to build around thoth.

To get the most out of the (since reworked) Thoth, you want at least 1 or 2 mana+power items to go alongside it (though there are some non-power exceptions, like Breastplate of Valor - but that's a situational pickup, great on some gods like Hel when building Book of Thoth).

The point is BoT isn't awful on it's own, it's just not as potent by itself as it was last season, and you get the most out of it when building mana+power items like (reaver, CDR shoes, poly, book of dead etc...). When non-stacking build paths exist, there isn't as much of a priority on stacking Thoth, especially when you aren't synergy building with it.

You don’t have to, either cdr shoes for the 10% cdr and mana to contribute to Book Of Dead passive or pen boots for the extra damage (especially early game).

Can always get cdr from other item sources anyways.