https://www.blackpoolzoo.org.uk/blog/big-cat-update
You will notice he does look a little different from when he left us. Before he embarked on his journey down south, he was given a contraceptive insert to prevent him from breeding - this can sometimes cause a temporary loss of mane due to reduced testosterone.
The implant has now been removed in readiness for him to be joined by his very own pride of females, shortly after he returns. His mane has already started to grow back and it should be fully grown in the next six months.
This article was from 2023 but it looks like his mane never fully returned. It does however appear that the picture was mislabeled.
The video here shows Khari more clearly- maneless but with darker shoulders and a more square head.
This article seems to label the image referenced correctly.
He felt confident enough to breed so hopefully he’s having a good time!
I don’t doubt it affects them more in the wild where something like this matters a lot more to them. Competitor males would feel more confident picking a fight I imagine and perhaps females would be pickier about accepting a maneless lion.
In a zoo setting they’re all comfortably fed and theres no competition.