Most of these products are usually 2-part epoxy based mixes, and thus do not require exposure to air or water vapor to cure. That is why they can solidify and cure so fast. The average DIY kit is 1-part, simply because the equipment needed to mix 2-part is rather expensive and finicky. 1-part either requires that a solvent evaporate out, or that something in the air reacts with the applied substance (usually water vapor).

2-part mixes are generally far superior in durability and ability to apply thick layers quickly, not just with bedliners, but with all kinds of epoxies.

If you've ever worked with polyurethane for woodworking, you'll know how much more effective the 2-part stuff is compared to the stuff you buy in a can. Same logic applies to the bedliner.