According to an article in the Daily Telegraph, Paris had a charter that said 60% of food in the village had to be vegan friendly & the day before the opening ceremony they ran out of meat and dairy options because they hadn't anticipated so many athletes choosing the meat and dairy options over the vegan-friendly ones.
The caterers were forced to bring in more eggs, meat and dairy products because not too many of the world's top athletes were touching the vegan diets.