You can sum up the reason in one word: procrastination.
Many people see the big difficult task they face, and try to hide from it. They mess around looking after small, unimportant things, waiting for the right time to fix the big important ones.
No time to start on improving your education, because you have to finish reading that paperback novel first? Can't exercise today because there's a good show in TV? Can't start working on forming new relationships because you really should call up your brother? Not ready to start that business because you're just too damn busy?
The biggest excuse people make for inaction is that the conditions aren't right.
"I can't get started now," they say to themselves, "because x isn't ready and y isn't just right yet."
Well, maybe they're not, but here's a wake up call - the conditions are never going to be perfect to get started. You can spend your whole life waiting for them to get that way if you want to.
You may have a headache, it may be cold out, those dishes may need cleaning, and you might not have enough money just now. So what? Get started anyway.
If you look for reasons not to start, there's always going to be lots of them. There's only one reason to get started right now - because the quicker you begin, the quicker you will receive the reward.
So ignore the thousands of possible reasons that now isn't the right time and get to it. Brace yourself for the problems, raise your stubbornness level, and get going.