The amount of time and effort an individual has to go through (the initial interview, subsequent follow-up, etc.) would be a substantial investment of time in and of itself. I have not heard of an employer who was willing to pay for the travel to an interview unless it was towards the final round.

That means one has to actually impress upon the potential employer his or her experience, and demonstrate a knowledge of the industry or work that one would be involved with.

With that much effort already put in, it seems like a lot research and effort to just get some free MR's out of it; not to mention the opportunity costs involved.

Wouldn't one just aim to get a job that actually one was actually interested in?

And I can't see this being possible for someone who is already gainfully employed, i.e. how can one take x amount of days of for these travel interviews?