So you have to weigh the risks of outsourcing to the risk of the whole thing becoming very late and very expensive. The risks around outsourcing are something further down the line, the risks of everything becoming expensive and late are something that will give the responsible politician a headache now.
What Dutch government/politicians seems to be "ahead" compared to other countries - is combination of narrow or short sightedness and (over)correction trough rules, laws and regulations.
Like giving subsidies and tax breaks for electrical cars, rooftop solar panels and mandating household switch from gas (LPG and such) to electric heating and cooking. And ignoring industry professionals for decades saying the distribution network won't scale.
More of the same with stuff like 30% tax rule for expats, which was originally introduced as cost saving measures because actually doing bookkeeping for expatriate expenses was costing government more money. But then more recently expat tax breaks have been reduced and phased out "because cost saving". Meanwhile employers have trouble finding highly skilled workers. And we're limiting numbers of foreign students in universities (by forcing them to do it in Dutch instead of English).
Some Bulgarians cheated/defrauded Dutch tax returns or such - and "solution" was ML/AI reviewing things - but it turned out to be broken/biased and (ab)used for other things - leading to the whole toeslag scandal and government resigning.
Same for nitrogen vs lack of housing... And many more.
If the private company is granted a defacto monopoly, it doesn’t matter that they’re a “private” company, they will have the same incentive and accountability problem.
What we know for certain though: Government taking over something is definitionally a monopoly and 99.99% of government employees are not subject to the accountability mechanism of elections.
Historically, the largest boondoggles of waste have always come from government, given they can legally hold a gun to your head and take 50% of everyones money to fund their “projects.” Private companies can’t take your money by force, unless being given those contracts by government. So again, the the incentive issue fundamentally arises from an entity being entitled to gather assets using violence rather than voluntary exchange.
IT is hardly something we need to do occasionally, so build up a department that can do it (not just write up huge reports about what it should do and outsource, like Logius) and invest in the people that will work there (retaining them as much as possible). Give a big middle finger to consultants, and listen to the tech experts. Build boring stuff that works instead of a new app every month.
It's not impossible in theory, and cheaper in the long run. It's impossible because asshats who would actually benefit from left and centre politics keep voting right-wing parties in to power.
So we end up with expensive consultants doing the work. Consultants have the wrong incentive. They don't want to stay in one place to long because it looks bad on their resume and overruns mean more money for them.
So really, I can see why a seasoned politician chooses the safest option for him. By the time an overrun occurs he will have moved on to the next job. I don't think left or right-wing politics has much to do with this dynamic. How will a left-wing politician magically get capable IT staff that higher paying industry can't even get enough of?