Of course, researching adult-size diapers will get you results for incontinence products. People who search for AB/DL also search for diapers, and as such the search results are correlated.
As for why AB/DL products wouldn’t end up in stores, the justification is pretty clear - it simply doesn’t make much financial sense. For most incontinent people who aren’t part of this community, their condition requires completely separate needs - discretion is often a must, and most would likely feel embarrassed with the babyish prints AB/DLs appreciate.
Moreover, most products sold in stores are designed as being a barrier for light incontinence, prioritizing light weight and value. These are the Depends and Attends of the world, the kind of things that are cheap and might hold a leak in an emergency.
AB/DL diapers, in comparison, are often are deliberately designed in the opposite direction - they swell and crinkle and squish, and are often design to hold liters of liquid more in comparison. AB/DL diapers are in essence “enthusiast-grade”, trying to push the limits with capacity, performance, and comfort.
This, in turn, drives up the price, leading individuals with heavy incontinence to invest in medical diapers instead. Designed mainly for nursing homes and similar care facilities, these diapers are often designed in between the two - they straddle price, performance, and weight, to meet the needs of that market. Many AB/DLs buy these products, as for a cost-conscious individual it can provide far better performance in terms of mL/$.
Now, let’s imagine that a normal store put AB/DL diapers on their shelf. Who would buy them? Normal customers who purchase cheap diapers wouldn’t go for them - they look too babyish, they cost too much, and they’re way too thick.
What about someone who normally buys medical diapers? They likely wouldn’t go for the AB/DL print, as the medical diapers are cheaper and more adult-looking to boot. Medical facilities probably wouldn’t invest in them, either, as imagine visiting someone in a nursing home and seeing a baby-block print out the edge of their pants. Some self-righteous individual would have a field day about that.
Finally, let’s explore the target demographic - the actual AB/DLs in the store. Would they buy it at the counter? It’s a product pretty obviously designed for this type of behavior and age play - would you be willing to go through a store full of normies, up to a cashier, and purchase it? I can imagine a lot of people wouldn’t, myself included. The current approach - delivering orders discreetly via mail - works just as well for most consumers. For the brands that exist - ABU, Bambino, Tykables, Rearz, etc. - they make good money from customers shipping the product to the home. There simply isn’t a motivation to ship product out across the country to stores.