Many different factors.
1. He may have been very ill or had an accident at one point. Things can change drastically in a very short period of time.
2. As we grow older, our priorities change, even moreso for some people.
One could assume he lost interest in modelling and staying in shape as he grew older, got kids and got new and totally different priorities in life.
Maybe he switched paths completely and became an engineer, doctor, teacher etc.
3. One really bad economical investment and lost money, became broke, lost a familymember (or more), got depressed etc
Stopped eating and training like he did.