Because Latin had three genders, from which Spanish only kept two: feminine and masculine and less frequent neuter, which is reduced to adjectives plus the use of "lo, ello, esto, eso or aquello."
Hay que ver lo valiente que es --- you have to see how brave he is.
Eso no es de lo que te hablé ---- that is not what I talked you about.
Masculine gender is mostly preferred in collective groups, but it can include both genders:
Los niños son traviesos (masculine, collective)--- boys are mischievous; children are mischievous. Only the context avoids confusion.
Las ratas son asquerosas (feminine, collective) --- rats are naughty.
The better question would be Why does English not have genders? considering that nearly every other Indo-European language has at least two genders if not three.
¿Le / les / te / os gusta?Words in black, in order:A usted (formal singular,both genders)A ustedes (formal plural, both genders)A ti (informal singular, both genders)A vosotros, as (informal plural - male, female)
Usted (you formal singular both genders)Ustedes (you formal plural both genders)Tú / vos (you informal singular both genders)Vosotros, as (you formal plural feminine, masculine)*Vos, in modern Spanish is dialectal. In classical Spanish it was formal but less than "usted" and the verb conjugation is different:Vos tenés; a vos te lo digo (dialectal modern Spanish)Vos tenéis; a vos lo digo (standard classical Spanish)
interesting, both genders, singular.
acordeonista (both genders)
Nicaraguense can be used for both genders.
The best (masculine plural or both genders)
The palindrome of "genders" is "sredneg." Palindromes are words or phrases that read the same backward as forward.
Tus primos (masculine or different genders) or tus primas (feminine).
Cantante (both genders) cantatriz (only woman)
In English, we don't have separate genders for nouns like they do in French, Italian, Spanish, etc.They are genderless as they are all usually preceded by a, an, the or a number.
English does not have masculine or feminine genders for words.
You say, "nietos." Arguably, it means grandsons, however, in Spanish, it's how they do "grandchildren," of mixed genders.