I've read the entire thread with growing anger and disbelief. OP, YABVU - you original post was bad and your subsequent ones much worse.
My father died when I was 8. It was rough. I have in my head a long series of memories of times I was very upset by circumstances and people in ways that were really entirely unnecessary had people give things a bit more thought. But time passed and I used to think I was 'OK now' in my early adulthood; much later I have recognised I am not OK, and never was (though luckily for me, the ways in which it has affected me haven't really held me back much). I had a couple of years of wishing away Father's Day and being very upset by it, and then when my mum got together with somebody else who ultimately was the most fantastic stepfather, I agonised each year over finding a card for him that said 'Happy Father's Day' without mentioning 'Dad' or 'Daddy' (the 80s were not a great time for inclusivity, things are different today).
I would've found it awful to be forced to make cards in school at either of those times. It's great that you feel you wouldn't have had a problem with it, OP - I respectfully submit you're probably looking back with rose tinted spectacles but even if I accept your words on face value, let me tell you that if this is the case you would've been in a tiny minority of bereaved children.
And I also have a different perspective. As an adoptive parent, I can now say to you that despite my own early life experience - actually, there are ('even') worse things to experience as a child than having lost a parent through death by natural causes as I did. My child has experienced much, much worse and is still living that trauma daily. This will be my first mother's day as a mum and all I wish is that it didn't exist at all, let alone being featured heavily in school. I have always loved celebrating my own mum but now I just wish my child didn't have go through the complexity of emotions it evokes in her.
And to the well meaning but frankly (and ironically) entirely unempathetic other poster who writes of using this as a learning opportunity to develop empathy - there is absolutely no comparison between this and discussions about different religions and there are many, many opportunities within the school curriculum already to learn about different types of families without anywhere near the level of unhelpful emotional charge generated by something like this, and also to speak sensitively and in appropriate forum about the nature of difficult life events. The PHSRE curriculum covers it fully and in an age-appropriate way for each year, but of course these subjects can also come up through literature, history and many other areas in the curriculum. ALL of these are much less painful, and much more easy to handle for those children directly affected, than forcing them through an activity seemingly solely designed to let them marinate in their painful feelings at an age and stage, and in a setting (in 'public' in front of their peers) where they are entirely ill-equipped to cope with it. And the reason I know about all these curriculum opportunities is because they are an active part of the ongoing dialogue I have with school about my child's needs and how they best support my child through getting an education with as little inadvertent harm being done to them as possible.
Only recently, we agreed it was better for me to take my child out of school for the day rather than they attended on the day when 1/3rd of the day would be spent learning about neglect and abuse via the NSPCC visiting (curriculum content I applaud for the other children but which would be actively harmful for my child at this stage in their life). So that was how we handled one circumstance and there are a variety of approaches schools can take to managing the needs of 'the minority' as you so charmingly put it. If they've made the judgement that on this occasion, not making cards during school time is the right answer, maybe you might like to try trusting their professional judgement and accepting you don't know everything and you certainly have a failure in imagination, basic empathy or both.