It's PRECISELY the reason you quoted!
The Spring Chickens are less likely to go into a molt in their first Fall, whereas a Fall Chicken is very likely to go into a molt its first Fall. If you do the math, that's a lot of egg laying time that one has to gain over that 6 months or so extra before their first molt. Further, since the older birds are going to molt in the Fall, the fact that you have young pullets laying all Winter is very positive, since your older birds won't be doing so- simply an economical thing.
Fall chicks also mature more slowly, as part of the oviduct maturing is regulated by the length of the day. Spring Chickens have the days growing longer as they go through their first months, and they'll lay younger than fall chicks, who spend their first months in ever decreasing daylight.
Brooding through the Winter can be difficult and messy, whereas brooding during warmer months is more likely to be outside and not so much a pain and mess.
The hens which provide eggs to the hatcheries are naturally going to crank out the eggs in the Spring, not so many in the Fall; shipping said chicks is far less risky for those hatcheries when temps are milder in the Fall, but supply may not be there. Fall can be exceedingly unpredictable and variable, as well, with very hot temps in some states and cold in others- that's hard to prepare for when shipping live chicks.
Lastly, many of us end up with broody hens in the Spring, and if you want to take an easy route to fewer roos to rehome, buying pullets from the feed store is a great solution to satisfying a broody's need to mother.
