This is what happens when optional formats try to become de facto standards. The HDR space has one default format -- HDR10. Every HDR-enabled device supports HDR10. Everything else is optional.
Aside from HDR10, the market is unsettled because both DV and HDR10+ are optional formats with varying degrees of industry support and added cost. Dolby is marketing DV as an indispensable upgrade. If they convince enough of the buying public, then it forces the market to adopt DV, even if it's not a mandatory part of the UHD specs. Samsung is a holdout, and they're a big enough player to at least create some uncertainty over DV's market prospects.
This is not much different than when DTS was originally trying to gain traction in the market. When the DVD format was finalized, Dolby Digital and PCM were the only audio formats baked into the spec. DTS was optional. But, DTS managed to get enough of the public to buy in that DVD players and AV receivers could only compete if they supported DTS.
Dolby and Samsung (the main proponent of HDR10+) are both trying to force a similar market compromise. It ultimately boils down to the tradeoff between the added cost (not just royalties, but meeting performance specs as well) and whether the feature generates added sales or defections from competing brands. This all takes time, and while the market is in flux, nothing's a sure bet. The slow uptake with DV reflects the unsettled state of the market.