There is a much simpler reason big code bases have less bugs. The size of the codebase is correlated with the investment a company is making into this codebase

There is a much simpler reason big code bases have less bugs. The size of the codebase is correlated with the investment a company is making into this codebase A larger code base will have seen many peer reviews from different Engineers over its lifetime, and as it is likely of the companies core products, a lot of testing, both internally by the test team, and externally by customers. On the other hand my hacky script, put together on a sunny summer afternoon, has zero love from senior management as they probably don't even know it exists.