There are two reasons
Performapals are the perfect deck to get used to Pendulum summoning they can swarm the field with a bunch of cute monsters, then act as a classic beat down deck from the good old days of Yu-Gi-Oh
Integrate into Your Collection These sleeves are built for both regular use and long-term storage, fitting easily into your existing collection system
They have the appearance of children wearing loose-fitting traditional Japanese garments, with long, unkempt hair
It's worth comparing the card to English-language Presentation Blastoise - another costly card lower down this list
The second most popular archetype, mono-green devotion, now includes Polukranos Reborn from March of the Machine but, overall, with the card pool being so large, only a small fraction of the new cards make an impact, thus greatly diminishing the Too Many New Cards effect