I absolutely concur with you. Apple is not caring about the consequences of having false assumptions that your children can't use some thing they still can. I am also having this issue and so are many, many others (just ask you friends who have Apple ecosystem and kids, or search this forum). Apple is totally aware of this issue, but chooses to do nothing for it. This problem has existed for many months now.
My child was on a camp and I couldn't be there monitoring the usage of her phone when the limits were again suddenly removed - she was secretly using social media and whatever sites (cause those limits were also gone) for the whole night at the camp with no sleep. Children are vulnerable to this kind of addictions so if there is a Screen Time system (which was good about a year ago) it should actually work.
And no - this is not caused by children knowing the passcode, I've seen screen time settings suddenly changing or disappearing on my child's phones when I am holding them with my children besides me.