Good standards take time.
Longer answer:
1) Writing a good feature proposal is hard. The best new proposals describe a clear use case and discuss multiple possible solutions with their pros/cons. Even just doing the research and putting together such a document be very time-consuming. Later, the proposal also needs formal spec text, Test262 tests, and eventually JS engine and browser implementations. Oh, and ideally there’s a transpiler plugin too. For some TC39 proposals, most of this work is driven by a single person.
2) New functionalities must be formally proposed (or “championed”) at TC39 meetings. There is a staging process, ranging from Stage 0 (the “hey, I’ve got an idea” stage) to Stage 4 (the proposal is shipping and merged into the spec), and each stage advancement requires committee consensus.
3) That’s right! TC39 operates by consensus, meaning anyone on the committee can single-handedly block a proposal from advancing or making it into the spec. This is great, as it sometimes prevents the committee from making mistakes that can’t be undone later, but it can also result in delays.