Comment by Gigachad

It does though, the exploit exists in memory. When you reboot the phone the memory is reset, if it's modified system files, the checksums won't pass and your phone will refuse to boot. Requiring it to be wiped and reinstalled.

These days most exploits can not persist through a reboot due to secureboot and other bootchain attestations. In the boot process, everything loaded gets checksummed and compared to signed signatures from Apple, but this only helps at load time, not while the phone is running. Of course if the phone is not patched, the exploit could be reloaded, but this would require revising a malicious website or reopening a malicious bit of media.