Besides the obvious system dependency reasons,the start sequence is historical.Dates back from way back pre DC3 days when pilots were still pilots and depended to a much lesser degree to their engine instruments(cause they had so few of them!) and/or any ground crew.
By nature the P1 sat on the left seat.When flying a multi engine airplane it seemed prudent to start the 'further' engine,hear its re assuring purr and then start the 'nearer' engine and again hear the purr before chocks off.
The nearer engine,needless to say would be the left or number 1 engine and vice versa.
If done in reverse order chances were that the right engine sound would be drowned in the sound of the left,therby not completely reassuring our 'fly by the seat of his pants and by the sound of the drone' pilot.
This is what info I have.
Of course one mustn't forget that these were the days when pilots litreally flew by the seat of their pants and were still aviators...
Sounds and sights were of paramount importance. And things never changed thereafter.Systems were developed so as to enable and support a right/left sequence.And a 4,3,2,1 sequence in quads.
Off now...
