Blockchain.com wasn't the one who built the first blockexplorer. By the way, they were known as Blockchain.info prior to that. You are right; no one actually needed to see the balance of someone else's address and most of the information that you see on the blockexplorers are not essential to most.
The first blockexplorer was actually created by theymos:
https://bitcointalk.org/index.php?topic=1727.0. This was before blockexplorer.com and it led to the creation of that which was a lot more polished and with more detailed information.
Was this happened before or after theymos become the sole admin of this forum, I believe previously the admin of this forum is satoshi himself. I always wonder why theymos was chosen to be the admin (since he is not the one founded the forum, --or maybe he is actually the one founded the forum, maybe he is satoshi--) but I if he was making the block explorer before everyone else then his contribution to bitcoin is what made him chosen to become the admin