I think the reason Senpai didn't have a "foodgasm" from Nagatoro's cooking while the girls got one from Senpai's cooking is because Senpai's cooking is the only one that was good enough to warrant a "foodgasm".
@Keansor Her cooking just wasn't up to snuff to do so. And this actually reverses the gender roles...usually it's the woman that's the better cook traditionally.