To be fair, most web/mobile frameworks expect you to do that.
Ideally, codebases would grow by adding data (e.g. a json describing endpoints, UIs, etc), not repetitive code.
- Commodity work, such as CRUD, integrations, infra plumbing, standard patterns.
- Local novelty, i.e. a new feature for your product (but not new to the world).
- Frontier novelty, as in, genuinely new algorithms/research-like work.
The overwhelming majority of software development is in the first two categories. Even people who think they are doing new and groundbreaking stuff are almost certainly doing variations of things that have been done in other contexts.