Because I personally think it's the optimal way for a person to live. It's also my way of doing my part to ensure that future generations have a world to live in.
It takes a lot longer than 6 weeks to fully adjust to any major dietary change, you were likely bloated from taking in far too much fiber and carbs.
No, there is proteins in everything. It just takes a little more time and thought.
Strength/Ensurance wise, I've never had faster improvements. I have no size or weight gains but I will say that a vegan diet is certainly not the most optimal for someone who is looking for size, not saying that someone can't build an impressive and large physique following a vegan diet.
Probably not what you intended but that came off as incredibly insulting as I personally see myself as having a very open mind.