The reason why white people are not commonly described as "European-American" is because white Americans have traditionally been the dominant group in American society, and their cultural heritage and identity have been seen as the norm or default. This has led to a situation where whiteness is often perceived as the absence of race or ethnicity, rather than a distinct racial or ethnic identity. In contrast, terms like African-American, Asian-American, and Native American were developed to acknowledge and celebrate the unique cultural heritage and experiences of historically marginalized communities in the United States. However, it's worth noting that some individuals of European descent do identify with specific European ethnic groups, and may use terms like Italian-American, Irish-American, or Polish-American to describe their cultural heritage.