This is because they stop your opponent from playing the cards they need to get to full power
Mayakashi Extra Deck Ykais The Synchro Monsters are side-unique and have 2 effects, following the pattern below: If your Synchro Monster whose original Level is [two Levels higher than its own original Level] is destroyed by battle or an opponent's card effect while this card is in your GY: You can banish 1 other Zombie monster from your GY, and if you do, Special Summon this card
Never forgive the hateful Lyrilusc There were no cards in the final set of Series 11 that could be considered significant new additions
Then, if you successfully used Millennium Ankh during the duel, the next time your opponent Summons a level eight or higher monster with 3000 or more attack, you can bring this back from the grave and get rid of your opponent's monster
If you can pull this off, however, its well worth the monsters required