It is relatively simple to quickly check all the commentaries "Does this commentary have an entry for this verse?" Likewise checking your dictionaries to see if they have an entry for a specific word. It is a simple look one place in the commentaries/dictionaries is there an entry for this. Even a large number of books can be quickly checked.
However, Reference books are not so easily searchable as the entire book must be searched from beginning to end since entries can be anywhere in a reference book that might be (if you could see it) a multi-volume tome. To mark the tab if the book contained a reference could take several minutes per book...Depending on the computing power of your machine and the total number of reference books you have it might take hours before there was a complete run mark each marking each relevant book (plus there is the matter of determining just how specific the reference must be in order to be worthy of marking entries).
It is simply a matter of the difference between checking an alphabetized list (or book chapter verse presorted list) as opposed to checking through mountainous volumes of data in totally random order. It would consume too much time and computing power to check each reference
Thus says the LORD, "Let not a wise man boast of his wisdom, and let not the mighty man boast of his might, let not a rich man boast of his riches; but let him who boasts boast of this, that he understands and knows Me, (Jeremiah 9:23-24a)
"Defenders of the faith are inclined to be bitter until they learn to walk in the light of the Lord. When you have learned to walk in the light of the Lord, bitterness and contention are impossible." --Oswald Chambers, in Biblical Psychology from The Quotable Oswald Chambers.