When I went I noticed how fat the bears were and this one is pretty bulky. Obviously good feeding throughout the year is responsible- I wonder if they hibernate in the UK climate- I would think not?
I reckon this one's about half the weight again of a wild North American Black.
Grizzlies at least are known to semi-starve through the summer, and fatten up in the Autumn. Whether other bear species do this I don't know, but I do know they stuff themselves silly in captivity given half a chance [well, you would, wouldn't you?]
Maybe a combination, both age and obesity. I noticed they were very sluggish too and that was several years ago. One sat immobile in the road for ages.