It's because they are not happening. There was one case where a single cell overheated, but it didn't propagate to the adjacent cells (and hence was pretty much a non-event).
With nearly 1000 787s in-service, each averaging around 4,000 flight hours/year (pre-pandemic), I'd say it's a pretty good bet that the redesign solved the problem...
Do you honestly think - with all the attention that everyone has been paying to the 787 - that there is a chance in hell that battery fires would go unnoticed/unreported by the MSM?