List is not in order of importance.
1. Your sister is almost thirty and she is way more fit than you are.
2. It's not fun to be referred to as the fat one.
3. You want a man who is fit...and want a man who can give a little bit more than what you have to offer. Fatties should be with fatties; dont' be a fatty.
4. If there is a zombies, you need better cardio to survive.
5. You don't want to be the weakest link.
6. You aren't getting any younger.
7. You aren't getting married soon and do want children. This will be difficult if your health is degrading.
8. Being healthy will boost your energy and confidence.
It seems to be all I have at the moment for my reasons and motivation.
I find people who are philomaths to be intriguing and intelligent. Surrounding myself with these types will be most ideal.