Often the answer is related to money. I won’t go into the different types of money or the idea that there is not enough - there is approximately US $37 trillion in circulation so there is more than enough. Hackers extend the effort because it can be an easy way to make money. Almost all attacks (hacking attempts) are automated. The reason behind the attacks runs from harmless to severe.

In the former, someone might just be trying to see if they can. Usually this is the domain of pranksters. If the attempt is successful what usually happens is that the homepage is defaced with no real harm being done.

In the latter, the website might be used as a springboard to infecting other websites so that the computing power of the server can be used for spam. Spam is a numbers game which is why there is so much of it. The website could be infiltrated with links trying to boost dubious and dodgy sites in Google so they come up higher in the search results. At its worst, the hacker could set up the website so it tries to install software on unsuspecting future website visitors with a view to extorting money.