Look at amino acid profile of these foods. Many of them do not provide "complete" protein. As in, they're missing some building blocks the human body can't fabricate.
It's possible to have a healthy vegan diet but it's a lot of work because you have to look at what amino acids and various nutrients are missing. It's much easier to just add meat to your diet. And anecdotally, a lot of vegans buy the "healthy" marketing and don't even pay attention to things like amino acid profiles. Which is unhealthy and frankly dangerous
It's possible to have a healthy vegan diet but it's a lot of work because you have to look at what amino acids and various nutrients are missing. It's much easier to just add meat to your diet. And anecdotally, a lot of vegans buy the "healthy" marketing and don't even pay attention to things like amino acid profiles. Which is unhealthy and frankly dangerous