Some people always like to ask why anime characters tend to announce what they’re doing, usually at high volume. Some suggest it has its origns in martial arts such as kendo, while other focus on justified examples like incantations and voice-activated weapons.
But at least as far as mecha pilots are concerned, this short scene from Super Robot Wars OG: The Inspector gives one other possible explanation.
(uploaded by Beta Food)
If you can’t see the video, or if it went by too fast to notice, the mech displays the name of the technique followed by the helpful prompt “SHOUT NOW!!” It’s kind of the inversion of a voice-activated weapon; instead of Kyosuke telling the Gespenst what to do, it tells him what to say. (This explains why literally everyone shouts when piloting the Mark II-S in the games, regardless of personality.)