Why do malware creators use such clever technologies for such silly purposes?

Various reasons:

Attacker is often not the Developer - Developers of malware sell the packages to anyone - the payload will be then defined by the attacker. Some attackers want to be stealthy - some don't, in fact some delight in being obvious and notorious.

Practice - developing techniques

Apathy/Ignorance - end users are really no good at fixing problems that can't be resolved by clicking on antivirus or malware cleaners.

Money - click-thrus and clickjacking can make good money. Viagra/Cialis spam also makes money. Fake-malware removal tool downloads can make a lot of money.

The answer is simple, and it's a similar phenomenon to the the anthropic principle, called survivor bias. There are many, many stealthy viruses that stay in place a long time, because they don't do this—but you don't ever hear or think about those, for the very reason that they're stealthy. Remember, what you're really asking is, "Why do I see so many non-stealthy viruses compared to the number of stealthy viruses I see?" But of course, you don't see the stealthy ones.