>>50829225They actually had a plan for it, but the Celebi movie forced them to scrap those plans and leave it with Kurt instead, never to be mentioned again, in hopes that that viewers would forget about it.
https://www.pokebeach.com/2008/07/second-pokemon-interview-with-masamitsu-hidaka-many-interesting-points>What’s the deal with the GS Ball? As I said “GS Ball,” he shook his head and started to laugh, embarrassed. He stated “You’re very sharp (for us remembering that, I guess)” and began to explain it contained a Gold and Silver monster. I asked him if Celebi was in the Ball (since you use it to summon Celebi in the Japanese games), and at first he paused, as if he shouldn’t say, but then said “Yes.” He explained that the writers were originally going to have a whole story about Celebi in the show with Ash and crew, and he made it sound as if the story was more important than the Ball’s function of getting Ash to move around (in fact, he only briefly mentioned the latter part; he was emphasizing the existence of the story more than anything). But, they decided to save Celebi for the movie instead, which is why that plot hole was just left there. He said the writers didn’t know what to do with the Ball after they made their decision, so they were hoping fans would just forget about it all together when Ash and crew left it with Kurt. My impression of what he was saying was that it was all just poor planning. I asked if we would ever see the GS Ball again, and he said no. I think we can safely say the GS Ball case is closed now. 
