If Zephyr jumps off a swing at its highest point, why does Zephyr move forward instead of dropping straight down?

Respond very briefly.
Zephyr moves forward instead of dropping straight down because, while on the swing, Zephyr gains forward momentum. Once Zephyr leaves the swing, the momentum carries them forward in the direction the swing was moving. Gravity pulls Zephyr downward at the same time, so Zephyr follows a curved path (a parabola) downward and forward until they land on the ground. The combined effect of forward momentum and the downward pull of gravity determines Zephyr's trajectory after jumping off the swing.