Protecting source code as important company asset, creates a significant barrier to start a derived initiative. Of course it is possible, the founders from SAP were once working for IBM and convinced they could do better.
With open source the barrier to start a derived initiative is mucwh lower. This explains the colorful diversity of more or less the same applications that originate from the same source. This phenomenon is named a fork.
Our advice, especially with open source, is to make a well considered decision. The higher your dependency on a specific application, the more important it is to have a substantial user group and large number of participated developers.
The feeling is not good, giving something to someone who benefits from it, without getting anything in return. Rationally however, this is not an argument to make no contribution back to the community. Especially by delivering extended functionality back, you ensure yourself from guaranteed functionality in the future.
The possibility to switch from vendor is an often heard argument and also mentioned in the previous paragraph about advantages of open source.
Consider that this is only the case when the number of users is substantial. Only under that condition multiple vendors will service the market of the open source software you are using.