It’s supposed to mean an increase in volume, but instead it now means a climax. Saying something will “rise to a crescendo” is a popular saying, I’ve seen many good writers say it, but it is wrong. The rising part IS the Crescendo, and the proper way to say it would be that something “crescendoed to a climax.” It is a specific musical term, with a specific musical meaning, and non-musical people have adopted it improperly.

Civilians can’t just come in and start stealing jargon words and apply their own non-jargon meanings. We rely on those meanings to communicate in that world. It would be like suddenly calling a tire iron a stethoscope, and not understanding why a doctor would think that’s stupid.