Pretty standard in highly regulated fields like aerospace, finance/banking or industry.

Sometimes for good reasons, like thorough validation need or operational constraints like spaced-out maintenance windows.

Sometimes for bad reasons, like a complete absence of unit tests and very old and brittle code bases requiring a lot of manual QA and several iterations for a version to be in a releasable state.

Incredibly common outside of startups and low-risk small-to-medium sized webtech shops.

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.

Nope. Banking.