That has the downside that a penny-pinching passenger might attempt to "hold it in" and then, shocked by a turbulence, involuntarily ejecting what was "held back"... leading to the plane needing an extra cleaning or being taken out of service.
There's a reason why even Ryanair, otherwise the leader in borderline unethical airline behavior, quietly buried their 2010 attempt to introduce a loo charge [1].
Another reason could be due to smokers. There's a reason toilets on airplanes still legally need to have an ashtray - there's still people who are willing to break the rules to have a fix so it's safer to at least provide somewhere safe to put a cigarette out.
Charging for the toilet could just encourage those same people to light-up in the main cabin.
I'm reasonably certain Ryanair was never serious about that. They like to make outrageous announcements anytime they think they are not getting enough attention for being the cheap airline.
I disagree that they're unethical. The deal you get with Ryanair is the ticket is as cheap as possible, then they nickel and dime you. A lot of people want that. A lot of people want better service, and they can go with a legacy carrier.
Do not give them any ideas, flying is miserable enough as it is. But here is another idea which maybe Airlines can do to make flying even more horrendous.
Eliminate the bathrooms and make everyone wear Depends. I would not be surprised this happens. The bathrooms could be replaced with a few seats and they save money by forcing people to clean up themselves :)
I now refuse to fly, I would rather drive or take a train or even a bus. Of course with covid driving is probably the better option if you can spare the time.
Of course I heard many people now drive instead of fly, which is making medium travel distances (say under 1000 miles) not enjoyable. Never mind the CO2 being pumped out.
Again the US needs a good public transportation system, which of course will never happen. If pols just stop talking about this, it would probably lower CO2 emissions from all their hot air they are expelling.
Worse problem: cleaning up un-capped, tipped-over bottles that are no longer full of pee after deboarding.