Wow. There's so much useful input on this board that I'm almost sorry I won't be a controller in 2021! Some of what I'm about to post is deliberately provocative (and, as I'm sure our provision at St Ives this year will testify to, not how I and Colin handled things this year).
Providing for vegetarians is relatively easy. Veganism is greatly more difficult, and currently remains a significantly small minority (that's an observation, not a judgement). While I am confident that all of the veggie food provided at St Ives was also suitable for vegans (and I know Colin put considerable effort into this), it is quite difficult to be absolutely certain, especially when it is not a vegan preparing the menu and thus familiar with the pitfalls. So on an event like this I think that it is foolhardy for the Organisation to state that vegan food will be available throughout or for a vegan rider to rely on it. To be honest, I find it difficult to believe that vegans think differently - there's too much at risk.
A similar argument could be made about other "extreme" dietary needs, such as gluten free and dairy free. It seems slightly strange to call these extreme, but the fact is that to someone who is not susceptible to gluten, or dairy, it is quite difficult to be sufficiently on the ball to confidently cater for those that are. I know that at St Ives the spread used on the bread was not dairy free (nor vegan), and we did not flag that up (it's only on reading this thread that I realised that).
While I have every sympathy with those who choose to, or even more so for those that have to, follow restricted diets, the responsibility has to rest with them, and at the end of the day they may have to eat somewhere other than the control. As amateurs in the catering business it would be foolish to rely on volunteer caterers to provide such specialist diets.
Having said that, I sincerely hope that we did indeed manage to provide something suitable for every single rider through our doors at St Ives. You may not have liked our selection, but hopefully it was edible!