Why do we always need to wait for 'launch windows' to get a rocket to space?

Artemis I launch has been ‘scrubbed’ a couple of times now. Why is a launch window so important, and what does scrubbing mean, anyway?

SpaceX debuts world's most powerful rocket, sends Tesla into solar system – Spaceflight Now

Peregrine Mission-1: First US spacecraft due to land on moon since the Apollo missions in the 1970s lifts off, Science & Tech News

Weather delays launch of NASA's billion-dollar Psyche mission to Friday – Spaceflight Now

To the Moon: NASA Lays Out Blueprint for Artemis I Lunar Launch This Month - CNET

More delays for NASA's astronaut moonshots, with crew landing off until 2026 - OPB

SpaceX's Falcon Heavy rocket launches asteroid mission for NASA

Rocket engines: the history & future of a test facility

Rocket Liftoff Aborted A Half-Second Before Launch : The Two-Way : NPR

Why do we always need to wait for 'launch windows' to get a rocket to space?

NASA's Space Launch System Will Lift Off - IEEE Spectrum

What exactly is a rocket launch window and how is it determined?

Tech it to space: Why do we always need to wait for 'launch windows' to get a rocket to space?