We have a sublime range of Unknown Origin Whisky here, all from the finest distilleries. Those producers just haven’t been named. Typically the region is stated, but it’s common for distilleries to sell whiskies to bottlers with certain restrictions, one being to not let them use their name.
There may be legal or contractual reasons, like agreements with other partners or distributors that prevent them from allowing independent bottlers to use their name. It could be strategic positioning, as selling whisky to independent bottlers without the distillery's name can allow them to cater to different price points and consumer preferences without diluting their primary brand.
It also might be because they want to protect the brand’s reputation, so only the products they oversee directly are associated with their brand or they want to avoid potential market confusion. It might stem from a concern that independent bottlers might comprise the whisky’s quality (for example, with a poor choice of cask quality) and distilleries may not want their name associated with these variations if they don't meet their usual standards.
But you can trust great independent bottlers to put top quality liquid in a bottle and market it, so don't be afraid to try a whisky without a distillery name attached. There's some real bargains and beauties out there!