I'm a parent and I sympathise with what you are saying hugely. Even in my group of friends we are all approaching our Y4 kids' work differently. Keen Mum has taken the opportunity to hot-house her kids, they are working flat out including through the Easter holidays - so far ahead, she is now coaching the Y4 child for 11+ exam.
At the other extreme Given-up Mum is so overwhelmed by the deluge of websites, logins and packs of worksheets we are expected to print, that she has decided to follow her own curriculum. To be fair, our school have not asked us to hand in any work, hand haven't really asked what we are doing specifically. We haven't had any personal contact from our class teacher but there was a generic email to the kids on 24 March. We have been told they are monitoring logins to certain websites, but they made it all sound optional so I estimate 90% of the class is ignoring most of what they send us.
It hadn't struck me the teacher might actually be worrying about what we were doing. All I hear from school is how busy they are, so I rather thought they didnt want to hear from us. I did email the teacher twice but had no reply, so I am joining Given-Up Mum, I'm now New Zeal Mum and I've decided doing my own curriculum tailored to my DD's interests, strengths and weaknesses is going to lead to the best results.
But I definitely read EVERYTHING the school sends, I'm up for hours at night looking at the materials, watching videos online, checking logins work etc. Its just that some days DD just hates the work that has been set.
Please don't give up and don't feel what you are doing is futile.
Another way of looking at it is - you are being paid to do this, so you should continue doing it to best if your ability, you are not doing this for fun.
Have you considered actually spending a day phoning the parents who you haven't heard from to see what the issue is? There may be some common themes you could learn from and improve how you are delivering content. It might simply be parents don't have time to send work in for feedback.