If you want to see the difference between schools which perform well and those that don't, have a look at the level of parental support for things like Sports Day....yes, even ones on a Saturday, when a whole year of notice has been given.
Have a look too at the level of support given by parents to things like a school fair.
In some schools, parents want to be supportive and don't see any school event as a cheeky imposition and the school as an enemy trying to tell them what to do. Those parents are also very busy, have other commitments and find it hard to respond to last minute requests, but given some notice will make some adjustments if possible and be there.
In other schools, parents quite simply aren't supportive and see the school as at worst the enemy and if not this bad, as some kind of cheeky organisation asking them for much more interest and support than they are willing to give.....so when the school puts on a talk about a topic of relevance for families with children of that age (with 6 months notice) only 3 parents turn up, or only 25% of parents go to parents evening, or the school knows it won't be able to put on many school trips because there wi t be volunteers to help boost the adult numbers, or a school fair cannot work or cannot be a bigger event because there isn't the parental support.
The OPs school clearly thinks Sports Day has a lot to offer to the kids....the staff would rather have the day at home, but they will go and work becaue they think it's worthwhile. They also think the parent body is supportive enough to make this work. Perhaps lots of people will decide that even though they had a year of notice, they will flex their right to say 'you can't make us' and instead go shopping, or go to their regular actitivity becaue they haven't been supportive of the school enough to think ahead and factor in that this event would be on. And perhaps next year the school won't offer it becaue there wasn't enough support.
We want our children to be at good schools. As parents we contribute hugely to those schools becoming or remiNing good through the level of support we show to things like sports days. If we don't support them and think that's okay or normal, then we have to accept the knock-on effects onto the whole experience.