Simply not Enough Material
Most DIY Bedliners come with about 1 gallon of sprayable material. If you review the coating calculation [1 gallon at 1 mil = 1604 sq ft / mil height = actual sq footage], you will see that 1 gallon is just not enough material to do a great bedliner job.
DIY versus Professional Grade Quality
You get what you pay for…. DIY bedliners are ok if you expectations are not too high. However, if you are looking for a durable, professional bedliner that can stand up to contractor grade abuse then a DIY is really not sufficient. Professional grade material applied in body shops by certified professionals is the level of quality needed to last in an extreme environment. Most DIY kits have insufficient material to properly coat a full size truck bed properly. On top of that these DIY bedliners are inferior in quality of material.
Spray-lining has identified this fact and has continued to go after large retail companies by offering a higher quality bedliner that comes with 2 times the amount of sprayable material.
Learn about Spray-Lining DIY Bedliners