you can't spend them on your costs
Picture the following: Atraxa is already in play, all of your spells are free, and most of your spells allow you to blink Atraxa and find even more spells to repeat this process with
Its like an expensive planeswalker that cant be attacked
Both cards have similar end results of cheating something into play, but Oath of Druids has certain deck building restrictions that Gamekeeper wouldnt have (e.g., creature tokens dont always play well with Oath of Druids)
Kinda like being stuck on two lands mentioned above, it is not much fun having nothing to play because youve ran out of cards in hand
Between all the cool cards you can open across those slots, you'll find that most79%of Commander Legends: Battle for Baldur's Gate Set Boosters have at least two rares or mythic rares in them, and 37% of Commander Legends: Battle for Baldur's Gate Set Boosters have three or more rares or mythic rares