Why is it important to focus on the public sector?

My research looks at engagement on public sector IT projects, so

Why is it important to focus on the public sector?

This might be a viva question and I can say that I justify this focus in the literature review (page 14) where I've written:
IT projects are important to the public sector because they are a key means of implementing government policy requiring often rapid changes to how the public sector department functions and provides services.
But maybe I've justified only the focus on IT projects, not on the public sector. The public sector makes policy and implements it through IT. Examples of failures of such implementation are:

• Libra system for the magistrates courts
• the National id scheme with an initial budget of £3 billion that went up to £5 billion.
• in 2003 the government introduced two credits: Child Tax Credit and Working Tax credit. The Inland Revenue's IT supplier created a new IT system for processing the tax credits, a system that went live in April 2003 with problems that took ten weeks to solve. Volumes were higher than expected and the testing window had been cut. Both suppliers and IR senior managers had to account for the fiasco to a Parliamentary Public Accounts Committee.

Public Sector IT continues to be problematic. The day after I submitted my thesis, a Public Administration Select Committee was interviewing IT expert witnesses on good governance and the effective use of IT (pd report is here). Witnesses pointed out that IS is there to implement government policy and government business change.

Hence, I see a need to focus on the public sector.