probably software of old where bugs are expensive, thus a thorough process was created, V model with consistency reviews; add manual hand overs and subsystem tests and you easily get months to production release.

PayPal started greenfield so they baked the qualification and consistency checks into the process and had it automatic. banks ho ooops.

Same for Tesla: they created a hand over free code to (testing) road flow. and they were capable of thinking like that because their roots are software.

GP below confirms traditional finance.