For starters, Outlast often felt too slow with its sorcery-speed restriction alongside its need to tap the creature itself
We also got a second way to do this with a bit more investment in the form of Warren Soultrader in Modern Horizons III, and that creature card is also a Zombie to satisfy Gravecrawlers casting requirements
For example, a Triskelion on the battlefield is 4/4, but a Triskelion in your library is 1/1
Second, the payoff is playing lands that tap for two mana, which is powerful, but at the end of the day, it's just another way of ramping into Primeval Titans, Eldrazi, and the like
And sometimes youve got 10 cards left in your library and 8 devotion on the board and you cast it to win the game the way the card was meant to be played
Even if I couldnt, a four-color commander gives you the ability to play all the cool cards you could want within his color identity