This is because its kind of a pain when it comes to mechanical play
By activating the cards effect to summon an Adventurer Token to your field, you can activate a copy of Fateful Adventure from your deck
Terapagos ex can hit for a hefty 240 damage all while your opponent cant OHKO it back, especially with a Bravery Charm [Paldea Evolved] attached
While this is worse, always entering untapped is a huge upside, especially for fast or aggressive decks
Casting a spell with madness ignores the timing rules based on the card's card type
Often, theyd be used as a useful adjunct for aggro decks, like Frozen Fish that would run a Merfolk deck backed by Lord of Atlantis and Winter Orb, or Stompy, an early Green deck with Mtenda Lion, Ghazban Ogre and Winter Orb