Why pubg Mobile hackers dont get ban?

The reason is so simple they just find the antiban values and block then so when pubg tries to detect the hack they wont reach up to hacker device as the hacker has blocked the way of pubg corporation to enter to there data to check for any changes.

How they do that?

They use different type of methods like host, lua scrip, firewall, libs, crc  and many more ways.

As one way of hacking is patched the hacker use different way to protect them from getting ban.