Whats cause the BBL results to look like a chicken butt?

There isn't a perfect answer here. If you are referring to having a lot of fullness to the buttock area on skinny legs, that would be an issue where the surgeon could have placed some fat into the posterior thigh to better support the BBL. It is possible to be a patient issue if you sat or laid on the buttock for a prolonged time after your procedure. If you post pictures, the community can likely provide you with a better answer.

Dear Zaa01,
it is hard to tell for sure, but in most cases, fat distribution is the main cause of poor BBL results. Fat viability depends a lot of surgeon technique. The fat has to be placed back into the buttocks as soon as possible so that it has a greater chance of survival. It has to be placed carefully so that not too much fat is placed in only one area.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

There are several causes of the phenomenon you describe. Some people also call it diaper but there is essentially a disproportion between the thighs and buttocks. It can happen due to both patient desire and surgical execution. Sometimes laxity can play a role but more often it’s overzealous fat grafting driven by Instagram aesthetics. It’s not an attractive aesthetic honestly and in the long term as people age, it can lead to significant aesthetic issues much like a breast implant it’s too large for the tissues.