That's one reason. However, I have been in the position of being desperate to sell a home (many people were at the time and in some places still are, I'm sure), and "test drive" or any equivalent simply does not make sense in some situations.
There's a lot less overhead to driving a car for ten minutes than there is to living in a new place for a day or two... to get the right impression of a car, you drive it in a residential area, you drive it on the highway, and there, you have at least an overview. To do the same for a house? Move in, settle in, meet the neighbors, live in it, then move out, because someone else wants a test drive, too.
And, of course, neither applies well at all to interviewing a person.
The metaphors just don't work here, and they're not helpful. Maybe there are things that work while car/house/pet/food shopping that can be applied to interviewing, but that correlation does not necessarily indicate any similarity between those situations, and comparison isn't useful unless the activities themselves actually are meaningfully comparable.
Most startups aren't looking to hire developers that are desperate for jobs. The point is they have a job they like reasonably well, they have other offers on the table from other companies. Other companies here did not require them to moonlight for a week knowing full well it might not work out (keep in mind they would be moon lighting with you in addition to interviewing with other companies). So why would they agree to moonlight if -- even without moonlighting -- the job offer is already a tough sell?
There are two possibilities:
1) You're looking for a co-founder of for perhaps the founding engineer, e.g., Sergey Brin and Larry Page hiring Craig Silverstein. You've impressed them to a great degree (they like your product demo, your background), and they are already willing to pay potential opportunity costs (a job at an established company, finishing their Ph.D. program, etc...) to join you. Then this really isn't a hiring problem per-se, this is a "finding a co-founder or founding engineer" problem; you are less likely be hiring someone "from the cold" for this in the first place (this is why so many companies are started by graduate students or former coworkers...)
2) You're willing to hire people who are unable to find other full-time work, in other words someone with no formal experience or experience in a completely wrong area (e.g., someone who worked on internal business web applications, but who wants to get into embedded programming).
Then you're really looking to hire an intern (in case of no formal experience) -- where the process is essentially that, a contract to hire, or simply take a calculated risk. In other words, you are able to see potential in this person (which they've demonstrated by perhaps building an app in their spare time) and are willing to set them up for success (as oppose to trying to find the best candidates out of a pool).
There's a lot less overhead to driving a car for ten minutes than there is to living in a new place for a day or two... to get the right impression of a car, you drive it in a residential area, you drive it on the highway, and there, you have at least an overview. To do the same for a house? Move in, settle in, meet the neighbors, live in it, then move out, because someone else wants a test drive, too.
And, of course, neither applies well at all to interviewing a person.
The metaphors just don't work here, and they're not helpful. Maybe there are things that work while car/house/pet/food shopping that can be applied to interviewing, but that correlation does not necessarily indicate any similarity between those situations, and comparison isn't useful unless the activities themselves actually are meaningfully comparable.