A few points should be made: - We don’t feel velocity, we feel acceleration/deceleration. While a sudden drop would feel crazy, if the jet rolled out and into the dive it may be subtle enough initially that the free fall was hard to feel. The pull-up out of the dive probably would have been felt, but! If the pilot came on the intercom and talked about weather, or if the attending crew didn’t act odd after the event, people are less likely to assume something weird happened.
Add to this the likelihood of IMC, as well as the likelihood that the crew warned of potential light turbulence - you’ll have a plane full of well-primed people who accepted the experience as “mostly normal.”
Add to that that there wasn’t likely wifi for another 10min or so, people may forget pretty quickly…
The graph looks wild, but people don’t feel that raw data. Perception is everything, and it is not that surprising that accounts of this event aren’t popping up like crazy.