Why can some instruments play chords and some can't?

Instruments that can play chords, like pianos and Guitars, are capable of producing multiple notes simultaneously due to their design, allowing for the formation of harmonies. In contrast, instruments like flutes or trumpets typically produce a single pitch at a time, which limits their ability to play chords. This distinction is primarily based on how the instruments generate sound; chord-playing instruments have multiple strings, keys, or valves, while monophonic instruments rely on a single airflow or string vibration.