Comment by culi

Bun had some early (imo, extremely deceptive) benchmarks that showed it had really good performance compared to Node and Deno. Zig was also a fledgling hotlang and Bun managed to translate the Zig community into more energy behind Bun. In addition to that, the creator of Bun became a minor celebrity for spending probably over 12 hours almost every single day working on it.

Everything just came together at the right time really quickly and they managed to capitalize on it.

Also at the time Deno had only just started to backtrack on npm-compatibility and it was still in its infancy (I'd say its fully mature today). Bun was ahead of that curve which made it immediately useful.