"just needed" is a simplification. Very few organizations outside the US federal 3-letter agencies have the resources to spend on volatile data recovery in practice. Even the FBI isn't going to bother unless they're confident some extremely valuable evidence is involved.
"The HotPlug's patented technology keeps power flowing to the computer while transferring the computer's power input from one A/C source (such as a wall outlet or power strip) to another (a portable UPS) and back again."
They were just unprepared. There was plenty of data to seize, but it was in RAM. They just needed the right equipment to do a cold boot attack [0] [1]
[0] https://en.wikipedia.org/wiki/Cold_boot_attack
[1] https://wootconference.org/papers/woot23-paper3.pdf