A natural explanation is that these hieroglyphs in fact don't look like aircraft to many people and that those that do think they look like aircraft are experiencing pareidolia.
I understand that this is speculative, but it is a speculative question. Other people have also proposed this same explanation. See here, here, and here.
One factor that contributes to the current appearance of the hieroglyphs (regardless of what that appearance is interpreted as) is the palimpsest effect.
Most Egyptologists strongly disagree that these carvings are anything but hieroglyphs. They guess that a recarving took place. Hieroglyphs were carved into the temple's sandstone wall. After some time, for whatever reason, new hieroglyphs were carved, but the hieroglyphs were only partially erased from the sandstone wall. Some of the old characters remained behind the new characters. People viewing the images today think the pictures look like modern modes of transportation. However, any resemblance to today's machines is simply a coincidence.
(From Ancient Astronauts, by Sue L Hamilton. p. 10)