I used to reload a lot of .45 auto before our wonderful Government banned such things and, of course, we all feel a lot safer as a result. (?)
There was quite a lot of small primer .45 ammo around in England at one time. I think it was Greek.or Turkish It had some unreadable lettering on the case. It definitely wasn’t milspec. no crimped primers etc.
Quite a lot of manufacturers in places like Greece and some of the former communist countries used to produce “semi surplus” ammo just to keep the plant running and to earn hard currency.
The size of the primer didn’t seem to affect the performance. There must have been some loss of ignition though.
I’m tempted to suggest it was done on the basis of cost but any cost saving would be negligable.
Some of the .455 Webley ammo which I think was made by Sellier and Bellot had small primers as well.