In 1998, when Google came into existence, other search engines like Infoseek and Altavista were indexing sites using the keywords meta tag. But, keyword meta tag, being a webmaster controlled parameter, can be easily manipulated to stuff it up with irrelevant and undesirable keywords.
While not giving any advantage to keyword stuffing, Google came up with the idea of using external links to rank the websites. Webmasters, having the older conception in mind, believed that Google too uses the keyword meta tag.
Thus, since its inception, Google had never used the keyword meta tag, since people started to stuff it up with keywords even irrelevant to their website. Other search engines might use it but Google, which is the major source of traffic for websites, don’t bother about it.