>>54034182A bunch of reasons. For english sets, WOTC had issues with printing and distributing 1st edition cards and getting them out the door fast enough. Many times, especially during later sets in Neo, the unlimited packs were the first ones to hit the stores, not 1st edition packs.
I have a good chunk of 1st edition cards in my childhood collection. But that's not because I was first to the store on launch day or because I was waiting for sets to drop, I just got lucky. It was very likely that I only got 1st edition cards, especially from Neo, simply because WotC was releasing 1st edition sets well after unlimited packs had been in stores for a few weeks already.
In japanese sets, 1st edition print runs were often the only thing they printed. I'm sure you've heard how rare it is to find unlimited versions of japanese e-series cards, they're far more rare than their 1st ed counterparts.