But one of the great things about open source and PostgreSQL's extension architecture is that these projects can coexist! pg_vectorsearch can work directly with pgvector's existing data types, so developers can use either index.
As a company, we want to move at a different pace and try things that a project like pgvector wouldn’t necessarily allow (and rightfully so). pg_vectorsearch is alpha-level software, while pgvector is stable. Releasing early is a way to make it available to the community sooner and getting feedback.
Then there are all kinds of technical reasons: different architectures, different implementation choices, etc. There's also the freedom to try new things and going in completely different directions.