is it compulsory to release it to the open source community?

No, it isn't. What you might want to investigate for yourself is the impact of the GNU General Public License v3.0 that Adapt uses and how that impacts on the licensing for any plugins you develop. A discussion about this has already taken place on these forums here, might be worth having a read through.

As Matt says, it is not compulsory. But I'd encourage (push?) all developers to make an effort to release their plug-ins to the public. Yes, it might mean a conversation with organizational leadership and setting up an organizational github account. Maybe even a sign-off process to monitor what is being made public.

Why? because every organization using Adapt has benefited from other people's work. There's no charge for using Adapt. As an open source project, Adapt depends on contributions of effort: code, testing, bug reports, documentation, sharing insight in forum posts, etc. A few companies are contributing to the project by assigning developers and developer time to coding. Many companies cannot afford this level participation. But many can afford to give back by sharing what they have created.