Here's why:
* Prestige and Standardization: Standard English, being the recognized and taught form of the language, is actively developed and expanded by lexicographers, writers, and language institutions. This includes adding new words, adopting foreign terms, and formalizing existing slang.
* Formal and Technical Language: Standard English is used in formal writing, education, and professional contexts. This necessitates a vocabulary that can accurately and effectively convey complex ideas and concepts.
* Regional and Social Variation: Nonstandard English varieties often have their own specific words and phrases that are not universally understood. They may have a narrower scope of vocabulary because they don't need to communicate in all situations that Standard English does.
However, it's important to remember:
* Diversity within Nonstandard English: There's a vast amount of variation within nonstandard English varieties. Some may have very specific vocabularies, while others have a wider range, overlapping with Standard English.
* Value of All Varieties: Every language variety, including nonstandard ones, is valuable and serves important communicative functions within its communities. They are not inherently "inferior" to Standard English.
In conclusion, while nonstandard English varieties can be rich in their own right, Standard English generally has a larger and more comprehensive vocabulary due to its standardization, formal usage, and continual development.