From their part in the Abyss storyline, to the capable midrange strategy they employ, but I would argue it is their relevance to design as a whole that gives them such importance
It has to compensate me for execution risk
Includes: 10 booster packs filled with powerful cards
Each placed card reduces the play cost.[On Play] De-Digivolve 1 1 of your opponent's Digimon, then, if DigiXrosing with 2 cards, delete 1 of your opponent's Digimon with a play cost of 5 or less.[All Turns] When this Digimon would be deleted, by returning 1 black level 4 or lower Digimon card from this Digimon's digivolution cards to its owner's hand, you may play 1 [SkullKnightmon] or [DeadlyAxemon] from this Digimon's digivolution cards without paying its memory cost
Whenever its destroyed or put into your graveyard, you can renew it to pass these great keywords along to another creature
Make it so that it can be targeted or that it can be destroyed by card effects