This is often made worse as a result of hiring outside consultants. Firstly they don't have the institutional knowledge you have when starting a project, but they also aren't incentivised to properly document and hand over their knowledge at the end since that means less future work.

This is why a lot of government projects take so long, they don't see the value in keeping an in-house team of trained experts (see the difference in train line contruction costs in the UK compared to Spain), until you realised how good they were but you can't hire them back.