This comes up from time to time. The shape of a baby's pelvis is a lot more rounded than most in-shape adults. One tape works ok to both hold up the crotch elastic and hold around the waist. This gets a lot more difficult when your pelvis gets more rectangular. You'll usually need two differnt sets of tapes to do each of these things well.
I'm not saying you can't get a good fit with single tapes, it's just a lot more difficult, and a lot less likely. It also means there's only one pull-point in the back instead of one high and one low. So you're a lot more likely to leak low because the pull point is in the middle in the back, and is providing a lot less tension on the back end of the crotch elastic.
So yeah, good for cuteness and "like baby diapers" but not nearly as functional as a usable diaper
I think a single tape can work fine--if done correctly. That means having big tapes and stretchy wings. As I see it, the need for multiple tapes on most adult diapers proceeds from a combination of relatively coarse-grained sizing (usually only two size for adults versus six sizes for children) and the near-complete lack of elastic. In other words, there's very little in the design of adult diapers to make them conform to the shape of your body, so the extra tapes are there so that the wearer or caregiver can size and shape the diaper as necessary. Now consider men's briefs underwear. There aren't multiple fiddly connections; you have narrow bands of stretchy fabric on your hips, and these are connected to single seams in front. Emulating this, but replacing those seams with single, large tapes would work fine. You wouldn't need huge panels of that granny-panty stuff either, since the tapes can be adjusted for adequate tension and the wings wouldn't need to slide over your hips.
TL;DR: I think the only reason we don't have many single-tape adult diapers is cost.
I expect it's cost of production and the fairly large number of people who can't get a good fit with them. They're a popular niche product in our community, but a niche in an already small market is risky. I was surprised how well Cushies and SDKs worked for me but I know that's not universal, so I don't expect to see a lot of variety in the one tape diaper market.
I would love single tape diapers, but I believe the reason adult diapers need 2 tapes on each side is that the hip and waist are different sizes. I do prefold cloth diapers a lot, and I have found I need 2 pins on each side because of this. I would love to use only 1 pin, but if I do they do not fit correctly nor do they stay snug.