The irony with SMD codes... (quote from The SMD Codebook)
"SMD devices are, by their very nature, too small to carry conventional semiconductor type numbers. Instead, a somewhat arbitrary coding system has grown up, where the device package carries a simple two-or three-character ID code."
When in fact, seeing the precision already present with laser-etched numbers on the parts, they could easily write actual part numbers with at least 5 or 6 symbols.
We already use magnifying devices to look at SMD parts anyway; it doesn't matter if the numbers are too small to read by eye.
I think there's probably two factors involved in the continued use of cryptic, ambiguous codes.
1. Habit. Started using codes when numbers could only be printed on. Kept using them when laser marking rendered size irrelevant.
2. Obfuscation. Codes are something of an impediment to reverse engineering.
Or maybe the time and power needed to laser-mark is a profit-margin factor?