Buffett recently said the annual real return on gold since Jesus's time would be about 0.2%/annum. I'm not sure what Exxon has done/is likely to do but probably a lot more than that. He tries to buy things likely to make 15%/annum hence no gold.

As an aside Buffett and others are very unfair to tulips. A tulip can produce many offspring tulips which can be sold for cash and currently account for about 10% of Hollands GDP. Many tulip bubble buyers may have done ok buying holding and sticking in compost. Try that with a bitcoin or a share of Berkshire.