Different Stack Pattern
The automated tests (also test frameworks) are implemented using a different software stack then the SUT uses. This will make it harder for developers to maintain the tests. I have seen web development teams needing to learn Java as an extra language, because the test team decided to us a Java testing framework without having the app developers involved. The testers where familiar with Java and not the PHP/JavaScript stack use by the other teams.
- Demotivates developers to write, fix and or extend tests
- Harder to maintain for a team
- Extra setup to run the test local (Tools, Runtime, etc)