Who is "email"?
This is just speculation on my part, but I think the absence of "important" information is simply evidence to the fact that God thinks differently than us. The story of the thief on the cross is not really supposed to emphasize the thief. Even when the thief interacts with Jesus, the purpose is to give credence to Jesus' innocence (even a criminal dying next to Him, recognized His innocence), to His authority as Judge (Jesus was able to grant the criminal entrance into paradise), His compassion as Savior (even on the cross, Jesus was concerned about influencing and saving others), and God's recognition of Jesus' innocence (Jesus would die and go to "paradise", not "Hades" or "Gehenna").
Still speculating, but I wonder if the anonymity further speaks to God's recognition of our weak nature and provision for it. Do you remember how the Old Testament Jews turned the bronzed serpent, which was used to save them during the wilderness wandering (Numbers 21:4-9), into an idol (II Kings 18:3-6)? God certainly knew our nature and that we would easily be distracted by the unimportant things, emphasize the trivial concerns, and maybe even worship the "creature instead of the Creator" (Romans 1:25). I wonder if He helped us by shrouding unimportant and distracting information.
Paul warned Timothy about "striving over words to no profit", arguing "fables" and "endless genealogies", etc. (I Timothy 1:3-7; 6:4-5; Titus 1:13-14; 3:9-11). Even if we did not succumb to directly worshipping these vain things, maybe God helped us again by not feeding our tendency to promote division through speculation. Certainly, He saved us from wasting too much precious time on such things, even if they never lead to division or strife.
Think about Paul's rebuke to those erring disciples, who took up a mythology and worship of angles (Colossians 2:18-19). Imagine how much worse and damnable error they might have invented, if they had been provided even more fuel for their speculations.
I think the striking sparsity of "interesting information" is God's way of keeping us focused on what is really important: Jesus, salvation, morality, unity, good works, etc. If nothing else, it proves that no man wrote the gospel story, because people love to embellish and tell colorful stories. Only inspiration could have rendered a story so concise and focused. Many people have used this amazing brevity as an indication and even proof of the Bible's authenticity and inspiration.
In the end, I have no solid clue as to why God left out that information. All I can offer you is my speculation.