You forgot to add the most important reason which should be at the beginning of that sentence - track record.

And also, hiding important financial details e.g. the so called "friendly fraud" case is not a serious mistake, which implies that somehow it all "just happened" and could have "happened to anyone". It was deliberate, a lot of people were complicit, and it is exactly the kind of issue that crosses the fine line between what is merely a "serious mistake" and goes and sits squarely in the realm of "intentional, systematic and deliberate fraud" to pump up the company pre-IPO. And the fact that this came to light about 7-8 years after the actual incident suggests that we have only yet seen the tip of the iceberg on these kinds of issues.

But let us suppose you are actually right that it was just a "serious mistake".

My view is that right now there are a lot more shady things going on inside FB even as you come and write this.

"Well, how can you be so sure?" is what people generally ask. That's exactly what people who were defending FB were asking as early as 2016 on these forums. But over the last 2-3 years, the skeptics have been vindicated, and those folks who were previously defending FB are nowhere to be found on threads which discuss Facebook. As the saying goes - their silence is now deafening.