The question is loaded.
The reason could be anything, possibly something unimportant. The key takeaway is, there is not much role for complete markings in modern days, because SMD parts are automatically picked and placed from reels; human placement is not used, so part identification is made on reel level: reel labeling is important, not part laser marking. Also products are not repaired by looking at what components happen to be used and buying replacements; ICs rarely fail anyway, and if they do, complete PCB assemblies are replaced. In rare cases where component level repair is being done, manufacturers assume that schematics and layout pictures are available to repair personnel. In any case, de- and resoldering such parts is specialized and difficult work anyway.
Some form of marking, which varies between ICs, is useful for automatic optical inspection to catch differences between a board and a reference golden standard board, but fuller part number does not add much value. Also any text makes it easy to visually confirm the orientation.
Many parts are available in both very tiny and larger packages, so it would be logical to use same typographical choices for both.
None of these are reasons not to add fuller marking, but are reasons why it isn't very important. So instead of explaining why not exactly, I'm pointing out they could ask you a counter question, why should they?