I think this is probably because most of the resources you are looking at were probably written by people from North America and Europe, where veganism and vegetarianism are niche lifestyles gaining in popularity, and where every veg*n is always being asked "where do you get your protein, then?" because large quantities of meat are consumed by the majority of the population.
I'm a British vegan, and I started working in a health food shop 14 years ago. It was the only place I could buy mung beans. I had one recipe for them in a vegetarian "student" cookbook.
As far as I know, thinking narrowly about the majority white culture, there are no traditional "British" dishes that use green gram. The same is probably true of the US.
Of course, there is an endless and wonderful variety of dishes that use mung beans in many forms from Asia. Not only are they a great source of protein that is high in fibre and low in fat, they are also exceptionally versatile and easy to deal with compared to many other pulses.
- Soaked and cooked whole and used as is or mashed into a pate
- Soaked whole and drained and left to sprout, then eaten raw or cooked in curries, stir fries, salads...
- Soaked and ground to make dosa batter
- Split and skinned and soaked and eaten in a salad
- Split and skinned and cooked to make a dal, smooth and thin or dry, sometimes combined with other pulses
and so on.
But the work of Asian chefs and cooks and bloggers who know all this is not so easy to stumble on online as the lists written by Europeans and North Americans, maybe because they are not writing explicitly about vegetarian sources of protein, but just about dishes they like to cook.
Searching for "moong" on this site alone finds 18 recipes :)