Lightroom presets are previously saved settings of the sliders and sections in lightroom that create a particular style. Initially, these were made for professional photographers to save time on editing photographs from similar scenes.
Presets made it possible for photographers to edit their photos and then copy lightroom settings to another photo or even a pack of photos in one click.
Later, Instagram blogging presets have become a way to express users by creating recognizable styles. Photographers like Peter Mckinnon, Alen Palander, Sam Kolder, Jordi Koalitic sell their lightroom presets and share their unique styles with the world allowing anyone to apply their settings to any photo.
Most of these presets are designed to use with desktop versions of Lightroom CC, because adding them to Lightroom mobile was quite a tedious task. Moreover, in the beginning, Lightroom mobile wasn't nearly a complete version of the original desktop version, and making presets mobile was kind of hard.
But in 2020, most users want to edit their photos directly in their phones without moving all photos to desktop, editing, then exporting and sending them back to their smartphones to simply publish a photo on Instagram.
Instagram still doesn't allow users to publish photos directly from desktop, so it's another reason while Lightroom mobile presets are in such a demand.
Still, to add presets to Lightroom mobile using a .DNG file is quite inconvenient and time-consuming.