1. "Your employees will do their best work when they want to work, not when they have to work. "
That would depend on the calibre of the employees' attitudes, and the work environment and culture.
So while your statement may be true, the thing is, many of them will not want to. Many people will slack to near zero if left to their own. The coffee maker won't even get cleaned. Not everyone of course, some are enthusiastic self motivators. But many in the workplace will slack to zero given the opportunity.
So if you sit and wait until they actually want to do their best work for you, you will be waiting a long long time.
2. "What are you doing to assure they want to come back the next day and continue working for you?"
Usually the employers provide them with whatever passes for local currency, plus maybe dental. At most shops this works like some sort of talisman. 'Natch the self-motivators tend to already be doing just what it is they want to, but for many of the rest it will be the only reason they ever considered employment in the first place.