The card quality and tutor effects are simply much more mana efficient so unless the combo deck has alternate uses for the specific draw spell such as a discard outlet or recursion effect it will avoid the latter in preference for the former
For example, if you play a Mountain and your chosen number is 2084750930, you'd only be able to cross out one of those zeroes
No Pokemon TCG trainer looking to make their mark on the world would be caught without at least a few of these powerhouse cards
Ezuri, Renegade Leader Ezuri, Renegade Leader was the best payoff for playing elves for a long time in formats like Modern
For example, if you discard a split card, you've discarded one card
It promotes early aggression and mid-combat trickery, which makes for an interesting alternative to all of Gruuls midrange and late-game beaters