It's just the simplest reason of ease and streamlining of manufacturing. Most ammo makers sell more 9mm than anything, the next tier (based on volume) is going to be .40, .45, .380, .38 Special. And of those, only the .45 used the different primer -- so why not standardize it to the smaller primer?Does anyone know the science or the reason for changing it to SPP from LPP?
If we rolled the clock back 110 years, I will certainly guess that the larger diameter case demanded or benefited from the larger primer. These days, it just isn't necessary. If the .45 ACP wasn't a 120 year old cartridge and it made it's debut right now, it would be a dumb idea to produce it with a large primer.
So it may be really annoying to a lot of handloaders but it makes very good sense.
There's another way that the ultra-annoyed MIGHT consider looking at this situation:
If you call up Starline and buy what you want, you get what you want. And if you buy factory ammo and you look at what you purchase before you throw money at it, you also get what you want.
And if you inspect and sort your brass, you get what you want.
With all these methods there are no hassles.
The hassles that seem to bother some handloaders soooooo much seem to happen when they are scooping up free brass and/or too lazy to sort and inspect.
There has been a lot of teeth gnashing over the what... 15 years we've been now dealing with SP .45 brass, but it's waning a bit.
It still annoys some folks. The only annoyance I have ever found with SP .45 brass is sifting through all the whining about it.