The Biggest Challenge Isn't the Math
One of the biggest challenges with helping students understand the “why” behind algebraic rules is often the attitudes about they bring with them to the discussion.
These are not attitudes that exist in a vacuum. These are attitudes that have built over time, often year after year in math classes throughout their pre-college schooling. A student may have had years of caring, compassionate, and considerate math teachers, but it only takes one bad experience to knock many of them off track. This is not to mention the very real systemic issues (including underfunded schools and systemic racism — not that those are particularly separate issues) that can get in the way of students' learning.
When you talk to someone who “hates math” (and trust me, I hear from a lot of them whenever I tell them what I do for a living), they usually tell a story of a particular teacher who made them feel dumb, or flawed, or “less-than” just because they “weren't good” at math. That one experience sticks in the minds of far too many students. It begins a snowball effect where a few less-than-perfectly grasped math concepts lead to frustratingly confusing math concepts, which in turn lead to an impenetrable barrier between the student and understanding.
Breaking down those barriers is difficult. It requires convincing the student to believe in themselves. That they should trust a process of learning that often involves failure. And it involves breaking down preconceived notions of mathematics as a binary field of study where everything is either “right” or “you're not smart enough to understand this.”
Any program or methodology that hopes to raise the bar and improve math aptitude, especially one that hopes to do so anonymously and asynchronously, must first accept that the math usually isn't the root problem.