Technically, it's invalid to say that technology has been around for 3000 years before the start of FFX. We simply don't know when the world began, and even then, how would we know that FFX's world developed in the exact same way as our own? Even if it did, it still took 10k+ years to even develop irrigation and simple farming techniques, another 5000 for the first civilizations to crop up, 3000 to the end of Egypt, 1000 to the end of Rome, and 1500 years to the current day.

For all we know, technology could've only developed for 100 years before the war (just look at our current situation, before machine power, we didn't develop nearly as fast as we do now, and the advances made in a year, would probably have taken 500 years at any other point). Where technology looms, war is not far behind. We don't even know why Zanarkand and Bevelle went to war in the first place, much less anything behind it. We know how, but not why, so it's a big difference.

All in all, it's quite simple as to why there's no internet, no space flight, or anything other relevant before Sin. Even if that technology existed, it was likely destroyed and covered up. As much as I would like to see FFX continued, the job that SquareEnix did on FFX-2 is enough for me to think it to stop. As much as I would love to sink my teeth more into the world, there's got to be a limit, and even though I believe in second chances, the way SquareEnix handled FFX-2 is enough for me to say "no more.". For everything possible that could be potentially good with an FFX-3, there's AT LEAST ten times more reasons why it's not a good idea.