Because it was the new thing the kids were doing. Go back 10 years and you’d fine people shitting on Minecraft for similar reasons. Couple that with the fact that Fortnite effectively cartoonified PUBG and became bigger than it and you have a perfect storm. Similar to Counter Strike players who hate on Valorant for being cartoony. I present to you this now legendary copypasta that summarizes things:

valarante child game… look to cartoon grapfix to make kid player happy like children show… valarante cartoon world with rainbow unlike counter strike chad with dark corridorr and raelistic gun… valarante like playhouse. valarant playor run from csgo fear of dark world and realism