How come networking protocols (SMB) are so bad at handling small files?

Dear experts, I've been curious about this for a while:

How come network protocols SMB (AFP, etc) handles small files so much slower than big files? Why can't, say, 100mb of binary data get bundled together and be sent in one go? And then deal with the permissions for each file in a bundled manner as well?

The difference in performance can be 20-fold between many small files vs. a large file transfer. I'm just curious how this can be a hard problem.

thank you! J