This is the 16623rd most frequent Korean word.
사안이어서
It means "because it is a matter/issue."
Here, '사안이어서' indicates the reason why everyone is paying attention to the issue - the issue's urgency.
이 문제는 긴급한 사안이어서 모두가 주목하고 있습니다.
This issue is urgent, so everyone is paying attention.
In this sentence, '사안이어서' is used to convey that the matter is the cause for not attending the meeting.
그는 이 사안이어서 회의에 참석하지 못했습니다.
He couldn't attend the meeting due to this matter.
Here, '사안이어서' explains the reason for careful handling by stating the nature of the matter.