Because people like Adam Maysonet were playing all Moxes and Balances and Armageddons, and killing people with Dingus Egg damage
Kefka, Court Mage Kefka, Court Mage caught on pretty quickly after the release of Final Fantasy
Not only do they send cards to the graveyard, which synergizes exceptionally well with reanimation strategies or mechanics like delve, but they also have basic land types, making them fetchable with lands like Scalding Tarn
Howling Mine is an important tactic to replenish lost cards
Nevinyrral's Disk [Wizard deck]: Before there was Oblivion Stone , there was this card
That being said, there are self-mill scenarios that can make it beneficial to stack Rad Counters on yourself too, particularly if you have any graveyard reanimation