SMB (Server Message Block) is a remote file protocol commonly used by Microsoft Windows clients and servers that dates back to 1980’s.
When it was first used, LANs speeds were typically 10Mbps or less, WAN use was very limited and there were no Wireless LANs. Network security concerns like preventing man-in-the-middle attacks were non-existent at that time.
Obviously, things have changed a lot since then. SMB did evolve over time, but it did so incrementally and with great care for keeping backward compatibility. It was only with SMB2 in 2007 that we had the first major redesign.
Jose Barreto has a new post that explains some of the history behind the protocol and outlines important improvements in SMB2, particularly in regards to reduced complexity, pipelining and compounding.