When a company tries to make a new software/services ecosystem (what WotC is doing here) there needs to be trust, because you're not buying a product you can use independently, you're paying for a 'live' service, if the company stops the 'live' service, you can't use it anymore. You can have spent hundreds if not thousands on such a 'game' with everything you 'own' going poof without anything you can do about it. Almost 50 5e books @$30 each, almost $1500 right there, subscription? Another $400 over the last 7 years... Then you have the potential to buy a TON of 3rd party stuff as well, all directly linked to DDB. And what exactly happened to D&D Insider for 4E? Is that still available? What is going to happen to DDB when the eventual D&D 6e hits? When is that ever going to happen? Another 10 years, what if sales aren't as good as they were and 'corporate' sees an opportunity to do a 6e early and kill off everything, so they can sell you everything again? It's not as if WotC doesn't deserve to have it's business model and potential new future products held to the light.
So much misinformation here.
First off, everything I've purchased on DDB is available to me right now on my phone because you can download copies of anything you want, and I have. So it could shut down tonight and I would still have all of 5e and my third party content. So much for that hypothetical.
When new releases supplant old ones on DDB, the old ones don't go anywhere. They are labeled "legacy content," you can access them whenever you like, and you can toggle them on or off.
WotC has publicly stated that they are sticking with 5e and letting it slowly evolve, and all D&D books will continue to be supported by DDB. So your hypothetical about a 6e is /shrug. Frankly, it seems like the standard arguments folks make about what they see as the pitfalls of purchasing digital content. But I'm pretty good with having content to all of D&D and a huge suite of tools for playing it for $7 per month, just as I'm good for getting access to basically all of music through my Apple Music subscription.
How exactly is that different from a DM scratchbuilding his own terrain, building/paint his miniatures and players doing the same thing? Or how much time do you think some DMs spend on good 2D maps? Self made adventures, etc. It's not different. But just because some DMs do this, does not mean everyone does this. And this is also true for building 3D scenes, it requires skills that the average DM doesn't have, it requires quite a bit of dedication and time to do it yourself and to do it right. Just converting a published adventure (like Vecna Eve of Ruin) to a (Foundry) VTT module takes a TON of time, and that's without having to make any of the resources (like encounters, the adventure, maps, tokens, etc.). Making anything beyond basic 2D maps also takes a TON of time, especially when you want the maps to have a consistent artstyle throughout the adventure. If you then start adding things like audio, effects, and new images to the mix the rabbithole is very deep...
As someone who has painted thousands of miniatures and builds elaborate sets using Dwarven Forge and everything else, but also sometimes runs games using the current map builder on DDB, I am assuming that the advantages of the VTT will be time, scope, and money.
In order to have enough miniatures and terrain to build most of the options I want, I have invested thousands of hours and tens of thousands of dollars over many years. Now
that's a rabbit hole. One I have freely chosen, but even bad VTT will pale by comparison. A good VTT can give players access to a version of all my analogue stuff for a fraction of the cost and effort.
Presumably, this VTT will automate most of the task, the same way the current 2d map tool does on DDB. That really is incredibly easy to use, and does in fact include all of Vecna: Eve of Ruin and many other adventures. If the promised VTT does a poor job then I imagine it won't succeed. If it does a good job but is too time consuming and technical, it might succeed as a niche option, like Foundry. Time will tell.