Children don't wet the bed on purpose. All children hate wetting the bed, even if they don't show any concern. It is embarrassing, it prevents sleepovers and disrupts sleep. They have no idea why they do it or how to stop. It is for this reason that sticker charts aren't particularly effective. Children aren't lazy or doing it on purpose if they are wetting the bed when asleep, or, if they are unable to wake up sufficiently to go to the toilet.
Parent embarrassment can also be significant, and this may prevent some families ever talking about it, going to the doctor, or looking into effective treatments. Many parents believe their four, five or six year old should be dry by now (especially when the first day of school looms), and they can put a tremendous amount of pressure on their child to become dry. This pressure can be counterproductive, especially if started at a very young age.
In the aforementioned study, there was a lack of awareness of the causes of bedwetting and 72% of the parents didn't realise that there are products that can be very effective to help stop bed wetting. Of course, some parents just hope their child will grow out of it, and some will, but others won't grow out of it for years. Only 55% of these families reported they would seek medical help to investigate the bedwetting. It is always important to go to your doctor to rule out any medical cause for the bedwetting.
As bedwetting is unconscious behaviour, it is very unlikely that any child routinely wets the bed out of laziness. Understanding that bedwetting is something your child cannot help, and that there are viable products and techniques that can either reduce the bedwetting, or, stop it completely, can be very reassuring for the whole family.
Schlomer, Bruce et al. Parental beliefs about nocturnal enuresis causes, treatments and the need to seek professional medical care, Journal of pediatric Urology (2013) Dec;9(6 Pt B):1043-8. doi: 10.1016/j.jpurol.2013.02.013. Epub 2013 Apr 19, Accessed 2016 http://www.ncbi.nlm.nih.gov/pubmed/23608323