"added, because" is correct and usable in written English.
You can use it when you are restating or explaining why something was added. Example: "I added an extra sugar packet, because I like my coffee sweet."
"I got in," she added, "because I earned it".
Not least, it added, because much more realistic and challenging games were more widely available.
"Probably," he added, because he wasn't positive.
He added: "Because I have the experience to do that.
He added, "Because she ignored me, I was doubly interested.
He added, "Because of CompStat, we need more arrests".
"It's false," he added, because it offers an uplifting ending.
"Univision, as a leader, has to be here," he added, because "Hispanics overindex on everything technology".
"They don't matter," he added, "because it's only the trust that decides".
But that was no real danger, he added, because the terrorist risk was essentially zero.
"I didn't finish art school, either," he added, "because of youthful rebellion and restlessness".
