Psyllium husk is a great blend of both, but it’s not very palatable because the insoluble fiber makes it gritty. It also tastes like dirt which is why Metamucil smothers it in orange flavoring.
You can get beans anywhere. If they are not available fresh, they are equally nutritous when dried or in a can. They are tasty, easy to cook, and an excellent source of fiber and protein.
If you don't like beans, how about a peanut butter sandwich. If you lack the requisite kitchen skills, ask a six year old to make you one.
The fact is that most people just prefer to eat other stuff. We prioritize convenience over health, enabled by food industries that profit from selling us junk.
This highly depends on location
If you buy fresh vegetables, I don't necessarily think they're pricier but they do require more planning. You need to buy what is in season, which means planning meals around what is in season and cheap to buy, which changes on the season.
For certain staples, buying frozen is extremely cheap, can be cheaper than fresh, can be better than buying fresh as frozen as soon as picked, and extremely easy to cook. I've always got frozen broccoli, carrots, peas, green beans, spinach in the freezer. Three minutes in a microwave steamer and it's an easy side, or add in to meals near the end of cooking.
I also always have a bag of potatoes in the house, cheap, keep well, easy to steam in microwave, can mash, can bake, pop in the airfryer etc.
Also, they're not more expensive for seasonal produce, last for ages frozen. Yes, requires more skill, but there are so many quick simple recipes anyone can learn. It's really a failing of the education system if people can't cook a couple of simple, tasty, healthy meals.