Points she made:
There was not that many people doing it
supply and demand
storage concerns
not getting enough money for the effort put in
hype sets being overbought
re-releases and consistent upgrades
She ain't wrong. It's why I was an avid reader of those terrible Facebook groups. Overwhelmingly they have no idea what they are doing, just hype each other. There is one particular old guy there that responds with decent advice, and I can't imagine why he's dumb enough to try and provide tips to direct competition and kill his revenue stream.
I can't count how many times I saw the AAT or Carnage "helmet" hyped. "Carnage will be bigger than the TIE Helmet" was common there. That set barely went on discount because they gobbled it up at RRP, and it sits at $10 over RRP on Bricklink and barely higher on eBay. Target did great on it. Once they had a hype train on a set I'd jump off it.
It's not just the number of sets bought, but the sheer number of people buying them.