* get practice at interviewing people for your role
* have an idea of what your market worth is, so they can use this in salary negotiations
* stop interviews being a difficult process they only do when you leave
* keep the option of finding a better candidate and replacing you on such occasions.
I'm going to take a wild guess and assume you would not tolerate that from your employer. It would show a lack of respect, trust, engagement, etc, basically it would convey to you that your employer doesn't even care about maintaining an appearance of giving a damn about you as a person. You've only just started there last week, and they're already thinking about firing you and replacing you with someone better.
Personally, whilst I think the attitude of getting upset because someone leaves the company is immature, I also think your attitude is disrespectful and shows such a contempt for the place where you're working, such an extreme lack of even the remotest sense of loyalty, that I wouldn't want to employ someone with your attitude ever.
This is without even delving into the fact that you're imposing a tax on the system, taking time away from your current employer (presumably with this attitude you're quite happy to pull sickies to cover your frequent job interviews), as well as other potential employers (interviewing people costs time and money; interviewing people who have no interest in changing jobs is a total waste of money for the company). If everyone suddenly behaved like you, regularly applying to even just a dozen jobs a year even though they have no intention of changing jobs, the recruitment process would incur such gargantuan costs that the economy would suffer, if not crash. Basically, your suggestion above seems to convey that you only really care about yourself. At least that's what it makes me feel from the really self-centred way you've described it.
I'm sorry that this reads like a personal accusation, but you made statements about your personal system of behaviour and I find that system deeply objectionable.
If I got the wrong end of the stick (perfectly possible), please do correct me...