Normally when people do a lease option, they know that the property could go up in value, or down in value. The owner takes that chance too. And a good option contract will fix the price, or the buyer shouldn't sign it in the first place.
Also, as to why people walk away from options after some time has passed, well, the job situation might have changed, or they don't really like the place after all, or they really would rather just rent.
Owning property is not for everyone--there's a reason it is called hoMOANership.

If you own, you may have to decide how long you will live with bad electric, or a backed up sink or whatever because you can't afford to fix it right now. A renter just places the call and if it is health-related, the landlord/owner is required to fix within a certain brief timeframe. For some people, that's worth it.
If your state uses a lawyer for real estate transactions, then yes, you'd want one. But in states where it's just real estate agents and title companies, you generally wouldn't need one. The title/escrow companies and the county will tell you about any disclosures you need, as will the mortgage lender.