Graham was too focused on price at the expense of quality.  

However, in hindsight, it was clear that the portfolio of quality companies is the best approach to stand up to any market situations.

Indeed, past financial crises confirmed that high-quality companies at reasonable prices perform better over the long term than companies which are straight cheap.

Buffett invested in very underpriced real assets in the beginning of his investing career.   After partnering Charlie Munger, he focused on higher-quality stock, proxied by the degree of competitive advantage they enjoy.

Many investors have gone down this same path of Buffett, practically all the value investors.  The main reason is that it delivers better results over the long term, although there aren't many studies to back up this assertion, making it initially a far from obvious conclusion.



Why have practically all value investors followed Buffett, preferring quality companies?

Maybe, when they are young and start out investing, they have an excessive desire to do well and make their mark.  They tend to favour the cheapest companies, which on face value offer the greatest potential upside.

With experience and maturity, and after having stepped on a few booby and / or value traps (cheap companies in bad businesses, which languish for years, failing to create value) and their economic situation improves, their tastes tend to shift towards quality, even if they have to pay a bit more for it.