if im being honest i think it was done on purpose, probably to show that there were others before maka and soul. Also both stein and soul suffer from madness, and if you think about it steins madness got worse when he left spirit, and when you notice on the flashbacks, spirits the one keeping stein sane just like makas keeping soul sane. its probably trying to show the close bonds they have even though they are a generation apart. but thats my opinion not fact. i just love spirit and stein though! ^^