> why camping is prohibited along a 230 mile trail.
Well, there's a huge amount of tourist traffic which could be damaging in very popular areas.
But really the problem is not someone with a small tarp stopping for one night. The problem is the millions of car campers. They tend to stay for several days in one spot and really trash an area. Yes, I know, not all are like that, but enough are. So 'camping' is forbidden.
But in this case, 'camping' really means 'car camping'. What we do is called 'bivouac'. Technically illegal, but often tolerated if you are very discrete and are only there for the evening. Very often you can ask the farmer and he will say 'over there'. At altitude (say >2,500 m) you would normally be ignored.
> Are there many gasthaus along the way?
Huts and gasthaus. That's what we had to learn the first time. We were doubtful that they would want us in their nice little gasthaus, all wet and muddy, but it turned out that >3/4 of the people staying were also walkers. We were told where to put our wet gear. It helps (a lot) if you carry some sort of UL hut slippers.