The biggest reasons why private schools are able to provide full curricula and Zoom lessons is because of the demographics they teach.
Private schools have no obligation to teach anyone; they teach kids with parents who have some money and are committed to education, and anyone who is overly difficult will get booted out (or managed out). The kids are in homes where there is plenty of money to spend on devices. Schools can set up a full-on timetable, safe in the knowledge that all their kids will be able to access it, that the parents will facilitate their learning and get them engaged and concentrating and doing all the follow-up work, and it is fairly unlikely that students would do things like sneakily recording the teacher and putting the content online for malicious purposes (and if any kid tried that, they would probably be kicked out).
State schools typically face a big range of families, ranging from middle-class education-oriented families similar to the above, to families where three kids fight over a single smartphone and the parents lack literacy or computer skills or cannot speak English much, or perhaps all three. And everything in between. They have to teach them and cannot pick and choose. Very hard to get everyone on the same page and learning at home--accessing the system, making sure the kids focus on the lesson and do the homework etc.. Teachers at state schools are wary of Zooming lessons because there have already been cases of students taking videos of content and turning into memes online etc. to harass the teacher.
Even if a school did put a full-on, "paced like a normal school curriculum" Zoom-enabled curriculum online with the attitude that "Well, we know that many kids and parents will not be able to engage with very much of this content, but we will provide it anyway and everyone can access as much as they want to or are able to," that's a problem, because you can't push ahead with a curriculum at normal speed if half your kids are barely accessing it and many of the rest are only accessing bits and pieces here and there. Because so much learning builds on what has gone before.
So: If you spend Week 1 reviewing and practicing times tables but only half of the kids tune in and actually do it, and then in Week 2 you start teaching long multiplication, that's a problem, because kids who didn't review their tables and are rusty, are going to really struggle when they try to do long multiplication. And so on. Most school learning is like this.
If you paid private schools to teach all the kids in this country, they would discover similar problems.
My nieces go to excellent state schools with excellent provision, but they are in a posh part of town with lots of privileged middle class families, and so the teachers are able to rely on the kids in the same way that private school teachers can.
Some of the poor provision that I have heard of on here is dismaying, but I do feel sorry for teachers in areas of high deprivation or even average areas---it is going to be really really hard to reach and teach all these kids. Part of me understands why some of them have given up and just sent out newsletters saying "Do gardening with your children! Mental health is key!!" etc. etc.