They are welcome to sue, but they'd have to justify their shenanigans to the court, which I'm sure would take a very dim view of intentionally tricking the user into signing up to something they didn't understand.
The business model relies on most people not escalating it there and making noise about it. If they start getting hit by chargebacks or start clogging the legal system with these cases it will end pretty badly for them.
Why would they need to sue? Can't they just send invoices to your email, followed by debt collectors?
The annual subscription is in plain sight. The cancellation terms are the result of bad web design for people using browsers whose browsers have made the idiotic choice to hide scroll bars by default (i.e. all mobile browsers and Safari) but that can be defended if the devs used Windows to make the website.
Actually, on mobile the terms and conditions get cut off halfway through a sentence so if you'd actually read them you'd see that they continue below the fold. Maybe that's not the case on iOS, though?
Their cancellation terms definitely suck but the terms and service and subscription term seem quite clear to me. "I didn't read what I was getting into" is hardly a defence. These details weren't hidden at all.
You can trivially ignore the debt collectors. If they still want their money after that, they can sue. At that point it's ultimately down to the court to determine who's in the wrong and who owes what.
The business model relies on most people not escalating it there and making noise about it. If they start getting hit by chargebacks or start clogging the legal system with these cases it will end pretty badly for them.