Using open source solutions in governments have many advantages. There are many reasons why governments are increasing their efforts in open source softwares.
No vendor lock-in
Open source softwares allow complete control of data and applications. Government entities are not locked into propriety formats. Furthermore open source solutions can be extended, customized and maintained with common standard and technologies.
Since open source softwares are available for everyone to try and test, most of the vulnerabilities are found more quickly and able to address immediately. Open source that complies with the current standard implementations focuses more in security.
Governments are not bound to the release cycle of the proprietary software release schedule and do not have to wait for security fixes and support.
Government can build something using open source tools. They can share their results to community and can also use the tools created by the community which facilitates reuse of components. If the governments use proprietary solutions, they have to wait for the companies to implement them.
Going open source is truly an advantage with lots of benefits to individuals and organizations. Many governments have realized this after going open source. There are famous examples such as Germany, UK and Brazil's government going open source. Some large tech companies such as Google and Facebook are committed to the spirit of open source software.