It lost 60% of marketvalue because there were not enough investment opportunities to deploy its massive cash hoard. The markets are supposed to operate this way, companies that cannot deploy the capital are supposed to return it to shareholders using share buybacks enabling shareholders to deploy their capital where they seem fit. Apple by contrast hoarded the money because they felt perhaps they can reinvest it somewhere more profitable but failed to find a lucrative investment target. Amazon on the other hand, kept on reinvesting their money keeping their profits suppressed rather than building a cash hoard, trying to build the infrastructure and assets that they believe MIGHT make them money (no guarantees though, there is always risk in capitalism and investments).
After that, because of oil price crashes, many of the investments didn't pay back as expected. When the value of your product drops a lot, the value of the employees also drops and so does the value of the assets and that is reflecting in the share price.
It the same for everyone, oil, gas, metals, lithium, steel, car manufacture .........
IF an oil shock occurs, the oil prices shoot up, then the share price will go up again and the market capitalization will return to its former high.
In hindsight, the share buybacks were not the best approach, but no one can predict the oil prices or shocks like covid or shale oil or financial crisis or renewable and electric cars, there are no guarantees.