From my understanding as a VIG for a good amount of years, it went away for multiple reasons. But the main two were as follows.
1. Some of the Vendors complained because it basically meant they had to be ready to go an hour early, everyone had to be there, and fully setup, and some of them wanted that extra hour in the morning to finish prepping, or to eat or to make sure their staff was all there etc.
2. VIGs would enter the hall and swarm a lot of places with convention exclusives or limited early-release products and things like that. So when the non-VIG people came running in they would encounter a line already, or a booth where the person shrugs and told them they were sold out for the day or in some cases the con already.
Now I know for a fact this early buying still happens. People inside the Vendor halls will often want something and will A. Allow their staff to head off to the booth they want and get the idea right before the doors open or wait till they open and grab the item and come right back to their booth. I know this because many have told me they have done it and I have seen it happen. So VIGS no longer do it, but Vendors still do to a lesser degree. But it's not as bad as it used to be when VIGS had early access.
And yeah the Swag bag has very much gone down in quality over the years. But that is due to many reasons aka. Way too many new VIGs have been allowed to join the program mostly starting in 2021 as means for a large cash boost for GenCon after 2020, so they need more swag to hand out, as well as rising costs for the companies. I am not sure if they donate the swag or if GenCon buys it at a discount, but either way, the swag quality, and quantity have gone down.