I don't know the founders and have not tried the product, but I'm building a business in the consumer subscription space so I'll post a few things that might clarify why they could end up with this model even with good intentions. I'll also add that I don't know much about the science/behavior of folks with ADHD, so I won't try to talk about that piece at all.
First, the app stores are pretty prescriptive about how you handle introductory trials on subscriptions (especially Apple), which means you are usually stuck with "start trial + opt-out" as the only viable model if you're billing through the App Store.
Second, behavioral/commitment theory often shows that for apps or really any behavior change that requires some effort, a longer time commitment/investment gets people to actually invest the effort they need to actually get value out of the product. If you let people pay for a month, they won't actually put in any effort and then at the end of the month they'll be like "I'm not getting any value here" and they'll just cancel. They won't put in the effort to build the habits. So most wellness apps/products (from meditation/fitness apps to gym memberships) end up with some sort of free trial period, followed by an annual commitment (and if there's a monthly option, it's at a steep hike from the annual one).
Finally, when you're early on in the life of your startup, you're mostly trying to get to product-market fit and see whether people are willing to use / pay for what you've built. You just choose a pricing period/plan that makes sense, focus on the product, then when you get the product where you want, you go back and experiment with finding the ideal pricing plan for you and your users.
That said, it's clear in this case that this model may not be great for the target audience (in fact, even for neurotypicals, canceling subscriptions and such is still a challenge to manage). And obviously the app creators could have put more thought into it.
We ended up with an opt-out free trial plan as per Apple's rules on iOS, with a monthly plan where the yearly plan is a 25% discount if you choose it, and several reminders before the trial converts to paid. We also allow users to do a standard opt-in plan if they're not signing up through iOS (ie only need to put credit card after trial expires). We offer refunds where we can for people who got billed but didn't intend to, but Apple has to process those refunds too.