A lot of these are much too complex for an aircraft roundel. They have to be easily recognizable at a glance from a distance. "Wait, is there a ring of crowns in there, or stars?"
An important point. One has to bear in mind the purpose of these. In OTL of course roundels have evolved depending on the combat situation the air forces found themselves in.
Some examples:
In WW1, Britain's Union Jack was too similar to the Germans' Iron Cross as seen from a distance, so we changed to a version of the French roundel (derived from the Revolutionary cockade) but with reversed colours, which is still used today.
Original British insignia:
German Iron Cross:
French roundel:
Replacement British roundel:
The Commonwealth dominions adopted symbols similar to Britain's but with more localised designs, as did the United States as it was fighting alongside the British and French in WW1.
Canada:
Australia:
New Zealand (not implemented until 1950s):
South Africa:
USA:
Followed by
The point is that these designs were chosen because they would look similar to the British (and French) ones and thus increase chances of friendly identification by trigger-happy allies.
Then, in WW2, the US and Commonwealth found themselves fighting the Japanese, whose 'meatball' Rising Sun meant that the red spot in the middle of the Commonwealth and US roundels could be mistaken for a Japanese logo by panicky gunners. So for the duration of the war the red part was removed from all the roundels - and the USA kept it that way afterwards.
Wartime roundel - Australia
Wartime roundel - Britain
USA
So it's always worth bearing in mind when designing roundels what wars the country in question fought with its air force, which countries were its allies and which its enemies - this will strongly influence the design of its roundel.