It's bad because if there's a particular piece I happen to want/need I've no way of knowing whether I'll have to buy 1 of those samplers or 15 in order to get it.
So don't buy the random sampler.
Why is it bad for me to buy it? Why is it bad that it exists? Why is it bad that different people like different things?
You claim something has to be physical to be real. Setting aside that data is physical, I think I understand what you are getting at. You seem to mean basically something that you can hold in your hand. Like a plastic miniature is real and a VTT miniature is not, in this instance. That's a pretty metaphysical argument, and I don't think debating the nature of reality gets us anywhere (I mean, both are icons meant to represent an imaginary character in a game, so the fact that one is made of plastic and the other is made of math seems like an arbitrary line to me). But what matters in this case is value. If I value a VTT as being worth X and am willing to pay that for it, then that is its value to me. Since we live in a market-based society, the ultimate value of a product, analogue or digital, comes down to what people will pay for it, regardless of individual opinions about what is real or what is not.
I own many digital things. Thousands of photographs, for example. I also rent many digital things, an arrangement that I am
very pleased with and think is better than needing to have physical copies in my hands in all kinds of ways. Pertinent to this discussion, I own most of 5e in digital form, and for $7 per month on DDB am currently sharing them with several dozen people. It would cost me a fortune to do that if I only had physical copies, not to mention the storage, wear and tear, and massive logistical inconvenience.
I also own tens of thousands of dollars of physical terrain and miniatures. That's a choice I've made, but I am aware that it is not a choice available to most players. Another VTT will give them new options, and why is that a bad thing?
So much of this argument just boils down to "I don't like this thing/it's not what I'm used to, and so it's bad." Or "junk," as another poster called it. But no one is presenting anything like a persuasive argument about why a VTT is bad on principle, other than that they basically don't like digital things or don't like random boxes.
Different people value different things. You can play D&D without any of it. No one can make you buy anything. If WotC makes a VTT that I think is worth the cost, I will pay for it. If they don't, I won't. If they decide to sell digital blind boxes of miniatures or whatever (which, to reiterate, they have never suggested and I very much doubt they plan), then I will consider whether I think they are good value, or not. Just like I do with everything else I purchase.