As far as I can see it's a logistics issue. I don't even live in the UK but germany has the same issues (3-6 months wait for therapy). There are clearly not enough therapists and those apps offer at least some help for people who can't get a therapist right now. It's better than nothing I guess. But doctors really need to manage this well who gets what kind of treatment. If you have severe symptoms those apps do nothing for you and you need more intensive care.