The landing gear was up because the crew left it up. This may have been on purpose to reduce drag (the flaps were also not extended). This can be done when the plane has lost both engines and needs to glide.
Landing gear have many failsafes, the last of which is to literally let them just drop by gravity. If the landing gear were the malfunction, the plane would’ve spent more time circling.
The landing gear was up because the crew left it up. This may have been on purpose to reduce drag (the flaps were also not extended). This can be done when the plane has lost both engines and needs to glide.
Landing gear have many failsafes, the last of which is to literally let them just drop by gravity. If the landing gear were the malfunction, the plane would’ve spent more time circling.