Practical or voluntary use - Those who wear diapers because of incontinence are probably not AB/DLs. While they may wear and use diapers, they aren't necessarily doing it to express an alternate self-image or indulge a fetish. This also applies to those who use diapers for practical reasons, such as astronauts and scuba divers. Finally, there are some who start wearing diapers as a "new kink."
There are many that wear diapers but are not paraphilic infantilists or diaper fetishists in the strictest sense. Their motivations and underlying mechanisms are different. However, those who share AB/DL interests and practices are generally welcome in the communities, and may sometimes be counted as AB/DLs.