#its lore

Humans and pokemon even alpha pokemon unless stated otherwise for pokemon cannot grow back limbs

Half pokemon of any type are the exception to the rule

Example Maxie as a teenager was taken by poachers his wings were pulled off and his tail cut off and taken

the poachers thinking he was dead just left him and closed up the cave

Maxie survived

The process of regrowing limbs is incredibly painful and takes time to fully complete in that time they are ravenous and barely holding onto humanity due to the pain they are in during the entire process. They are incredibly dangerous during this period. Depending on the severity it could take longer then a month or shorter

Another example when Ariana cuts off her talons aka a full digit off her fingers it takes about two weeks to grow back

Maxies took almost half a year to fully grow back

Emmet got an ear cut off from battling took a month to regrow