Do doctors give us proofs for medicines they are giving us? Do civil engineers give us proofs for the quantity and distribution of steel in houses?
If they (the maraje) want to give the proof for each rule, rules book will be more than 40 volumes.
Are you ready to read 40 volumes, and understand them?
On the other hand, can you understand them?

All the proofs, or the way to get the rule are given in the detailed books, while the rules book contains the rules only, because it is written to be applied.