But these orthographic distinctions are meaningless to anyone who does not understand the concept of palatalization in the first place! You have to understand the difference between ль and л before you can even start to understand the distinction between ля and лъя and лья.
And do you know what will happen if you include an in-depth explanation of palatalization in your beginner textbook? No one will buy it, they'll buy the one that teaches them how to stumble successfully through a simple conversation, because that's all they want to be able to do!