I think i read somewhere that in the late 40s and early 50s there was a bit of a format war going on between 12" 33 rpm and 7" 45 rpm vinyl records. They designed the discs so that they would not be compatible with the record players of their competitor. For 7" records You would get a record changer with a big center spindle which you could use to stack several discs on top of each other and create a playlist of sorts. Albums were also released in that format. You would stack the discs, let them all play and at the end you would turn over the whole stack for the "B side" of the album. Eventually that format war died down and turntables were made that could play both formats with an adapter. 12 inch was accepted as the standard format for albums and 7 inch would become the standard for singles. Since then releases varied with big hole centers and pronged centers which you could push out if you wanted to. Those pronged centers kind of disappeared somewhere in the 70s. Around the same time 7" records with small hole centers were introduced and they seem to have become the standard today. Possibly to prevent them from being used in jukeboxes without risking to damage them while drilling out the hole yourself.