Though unusing hiragana fonts saves space, it had been deliberate given all other Konami games use hiragana.
Pre-1945 Japanese army & navy almost always used katakana instead of hiragana because official documents eg Meiji Constitution usually were so (see here). Also telegrams like Tora Tora Tora were & still are always transcribed to katakana without kanji. Therefore a text spelled in katakana, which is unorthographical nowadays, looks very classic and "military" to the post-1945 Japanese population.
Same can be said about the typewriter sound heard after every character which is after the sound effects in old American film/news.
I think the inspiration comes more from daisy wheel printers.
The old documents were written by hand or with the rare typewriters that only had KataKana.
In the '70s, the daisy wheel printer was futuristic, but Metal Gear is not from that time.
However daisy wheel printers with KataKana only too were probably still commonly used by the military until very late.
