partly because; also because of ~
This pattern expresses that something is one of several reasons for a result, often with an implied nuance that there are other reasons not mentioned.
こともあって means 'partly because' or 'also because of'. It is used when you want to say that one factor contributed to a result, but you imply that there are other reasons as well. It often appears in explanatory or narrative contexts, giving a reason for something that happened, was done, or is the case. The pattern is somewhat formal and is common in written Japanese, news reports, and polite conversation, but not in casual speech.