It's not so simple as many think ....
For one thing, you need a way to ensure that the GPS signal remains valid during the approach. Otherwise you may find yourself following a dead reckoning course without noticing that, absent software that generates a loss-of-signal warning. Also, you have to survey the area around the destination to ensure obstacle clearance, including the area used for a go-around. There's a lot more to this than just drawing a couple of lines leading to the runway with waypoints at various altitudes, although that would usually do the job, yes.
I distinctly recall operating with a little GPS unit that only gave left-right guidance, combined with sighting various visual points that let us descend to something like 150' AGL in thick African dust haze to land on a rather short and narrow air strip. That was something everyone just turned a blind eye to, since it was the only option for getting into that particular strip. It took a peculiar combination of skill and stupidity to do that day-in, day-out, but as far as I know, nobody ever crashed doing that particular approach.
On the other hand, I remember a crew that was fairly new in-country who found a radio mast with a Gulfstream II in pretty much the same way it seems this German accident crew found that high-tension mast. They were taking a short-cut into an airport that did happen to have approved approaches and they must not have known about an isolated radio mast that was located not far away from their destination, but well off any approach path. They knew where they were, sort of, but they did not know where that radio mast was, or perhaps even that there was one there, so that they probably popped out of a small rain shower to find it waiting for them, even assuming that they saw it at all.
It sounds crazy, but it's very often so that you take risks because, while you can never prove that you prevented having an accident, it's easily proved that you did not make it into your destination.
I have been lucky in not having to fly for many VIPs, but I did notice a certain amount of pressure when I did, pressure that seemed to come from some lack of understanding of reality that applies to the rich and powerful the same as it does to everyone else. It's this, "What do you mean by, 'You will have to take a taxi, Boss; we can't make it in to Hackelschmackeldorf International today.'? Do I have to find myself another Captain, one who can manage this simple thing? I have an important appointment, but now you expect me to show up for it an hour late, in a taxi instead of in my private jet? What am I paying you for?" And so on and on. I guess you have to have been there, to understand how an experienced crew can make such a stupid mistake with such deadly consequences, going VFR in IMC, especially when that is something we teach beginners to avoid completely.
It's like being taught not to drink and drive, something that seems quite obvious, yet we see people doing exactly that, all the time.