because of ~
This pattern expresses an additional point that compounds a situation, often with a tone of frustration or emphasis, meaning 'and on top of that ~' or 'and what's more ~'.
This is a fixed expression used to add a reason or characteristic that makes a situation even more extreme or problematic. It carries a nuance of 'and on top of that' or 'and what's more', often implying that the speaker is a bit annoyed or resigned. It can be translated as 'and that's why' only in the sense that the added point leads to a conclusion, but it is not a simple causal connector.
It appears in both written and spoken Japanese, but is more common in formal or narrative contexts. In casual conversation, it might be used for emphasis.
For example: 雨が降った上に風も強い。 could be rephrased as 雨が降る**と来ている**上に風も強い。 but that is not typical. A correct example: 彼は遅刻する**と来ている**から、困る。 means 'He is late, and on top of that, it's a problem.' But careful: the pattern is usually used with a following statement that shows the consequence or evaluation. The と here is a quotation particle, not conditional.