This is the 13893rd most frequent Korean word.
많았는데
"많았는데" means "there were a lot (of something), but/though..."
Here, "많았는데" is used as a past tense description of quantity, indicating there were many people at the event.
그 행사에는 사람들이 정말 많았는데, 분위기가 활기찼어요.
At that event, there were really many people, and the atmosphere was lively.
In this sentence, "많았는데" refers to a past condition involving a large amount of budget, followed by an explanation or contrast.
예산이 많았는데 계획을 잘못 세워서 다 써버렸어요.
There was a lot of budget, but due to a poor plan, it was all spent.
Here, "많았는데" expresses a past scenario of having numerous opportunities, leading into a reflection on preparation and outcomes.