but I wonder why notams can't be uploaded automatically and compulsoraly onto your GPS so
AFAIK almost all NOTAMs contain lat/long information in a standard format, although this information is not always present in the NOTAM overview (which normally only shows the free-format text field). Exceptions of course are things like whole-FIR NOTAMs.
Technically therefore I don't think there will be major problems to implement something like that. You might need a little more internal memory, but that's about it. In fact, I just googled a bit and it looks like the PocketFMS team already has something like this on their to-do list.
Furthermore, there are several "amateur" websites that already do something like this. It's just a matter of implementing that in a GPS instead of a PC. So there's proof that it is *possible* to interpret the data correctly. (
UKGA home and
NotamPlot v2 are just two examples.)
As far as making things mandatory - that's going to be difficult. First, of course, it requires everybody to have a suitable GPS - in a day and age where only an ASI, ALT and compass are mandatory for VFR flight. Then the GPS needs to have some sort of interface (via the PC and the internet most likely) to a suitable NOTAM database and this interface needs to work "on the road" as well. Anyone who has tried doing some sort of PC-based flight planning on the road, using WiFi, a cell phone interface as modem, 3G or something like that knows that this is not exactly trivial.