IMO, doesn't really matter. Even if they keep buying new software that gets published as OSS after 5 years, it's still benefits the public.
Also, other companies could reuse the code, even if it's after say .. 3 years. It would also be a boon for transparency, and also lower the bar for alternative suppliers.
Over here, it's almost a meme that the government procures software that noone but the original supplier has a right to modify, which naturally results in enormous maintenance fees. Often they even procure new SW, because it's cheaper than the maintenance fees of the old one.
Are they going to set up a software engineering team to extend the program they bought?