The low toughness is a significant vulnerability but the flash and hand manipulation both mean you tend to get good value even if the card dies at the first opportunity to Arc Trail or Lava Dart
Be it a reanimator deck that needs self-mill, a storm deck, or a Splinter Twin + Pestermite combo deck, blue is usually involved somehow
With how small windows of opportunity are in cEDH, one turn is often all it takes to get there and win especially when the extra turn you take can be between two opponents turns oh yeah, its an instant
For a new player, it is really exciting at first as you get to try a lot of different variations and get a glimpse of the depth of the game usually also playing against people at the same level in matchmaking
Rakdos's Return provides all that value while scaling with the game
Most extra-turn spells cost five mana or more, which explains why its such a massive outlier in power