In my experience (math teacher at a community college for 20 years and former Ph.D. student who quit before finishing the thesis) the overwhelming majority of people can not learn mathematics properly from a textbook. They need a teacher or someone to help with problems. It's very difficult to get to a point of really understanding the definition/motivation behind concepts. Even with a teacher it's hard to understand.

Here's a simple example. The distributive property says:

a (b + c) = ab + ac

I can teach students to expand 3(x + 2). With some practice almost all of them will get this. They'll say

3(x+2) = 3x + 3(2) = 3x + 6

Do you know how hard it is to convince people that due to the nature of equality you can reverse the steps? Some never understand that

3x + 6 = 3(x + 2)

Some will never understand that 3x + 2x = 5x because of the distributive property and that combining like terms for the expression 3x + ax is the same process.

I don't think there is any desire to be elitist in terms of having good books that are appropriate. It's just hard to do. We've gone through various cycles of reforming calculus, introducing old concepts in a new way. Through all of the changes one thing has remained constant in my experience. The percentage of people who can get it remains the same.

I do agree with your point on providing solutions.