I don't see why.Well the audience also expected All Might to say it.
EITHER WAY it would have been better than 1 million percent
All Might saying Go Beyond Plus Ultra in the Nomu fight is cool because he concludes with that punch an incident that started from people thinking "All Might is weakened now" and planning their attack around that so he literally has to go beyond what was expected and because it sets the tone for the idea that great heroes will always make it out of a pinch, which was reiterated here with Midoriya thinking about those words and is presumably what the students will go on to prove as the series goes on and they show their worth when put in tough situations. Having Midoriya and all the other students say "Plus Ultra" every time they go beyond their limits in a pinch would get tiresome. It's enough to simply know that these moments and final attacks represent them going Plus Ultra without having them say it all the time.
I don't need to have the motto screamed out loud all the time, just it being lived up to is enough. It's like asking for Naruto to end every arc shouting "Will of Fire" or Luffy to finish everyone off with "Will of D". It's stupid.