Jin Air plane carrying 156 people returns to Incheon Airport after departing for Vietnam... Why?

A Jin Air passenger plane heading from Busan to Vietnam was forced to return to Incheon International Airport due to a bird strike shortly after takeoff.
At around 8 p.m. on the 21st, Jin Air flight LJ115, which departed from Gimhae International Airport for Nha Trang, collided with a bird after takeoff.
The bird strike occurred about an hour after takeoff, and sparks and smoke were reportedly seen coming from the engine.
At the time, there were 150 passengers and six crew members on board, but no casualties were reported. Since it was not possible to fly to Nha Trang, the passenger plane was landed at Gimhae airport to meet the maximum landing weight.
After using up fuel over the airport, the plane landed at Incheon Airport about three hours later at around 10:48 pm. Jin Air said, "We returned to Incheon Airport instead of Gimhae Airport, which has a time limit for nighttime takeoffs and landings.
"We conducted a safety inspection of the aircraft," he said. "It had not been long since the plane took off, so it was full of fuel. We used up the fuel and reduced the weight so that the plane could land safely."
"After turning back, a replacement aircraft was deployed and the flight departed four hours later than scheduled, at around midnight today (22nd), all passengers were on board.
"I left for Chan," he explained.