If the company earns money, and I own shares, shouldn’t I earn money via dividends?
You do. Companies give dividends all the time (well, every x months, usually at least yearly).
It looks to me like the only way to make money is to buy low and sell high? Or is that just greed?
Just greed… mostly. A lot of people want to “get rich quick”, and a bunch of already rich people like to gamble to get even richer, so a lot of market volatility comes from greed… but a share price with good growth expectations can make it attractive enough that the company may decide to give lower dividends (no need to attract people), so if you can “buy low, sell high”, you may still want to do it regardless.
You can still ride the market mostly on dividends by diversifying and investing into multiple companies whose share prices will average out in the long run (picking the right diversified portfolio, is an art on itself).
need to make more next quarter
That’s mostly an effect of tying C-suite compensations too closely to share prices, with no further checks in place. When the main driving force behind the decision makers is increasing share prices, they’ll happily burn down the whole company, cash out, and jump ship.
Sometimes it’s done on purpose, when some long-time investors grow tired and decide to cash out, maybe because they expect a change in the market and the company becoming less competitive or even obsolete. If the expected changes are big enough, it’s easier to start a new company from scratch, than to restructure an old behemoth with thousands of people used to doing things “like they’ve always been done”.