A key aspect of P3 is retaking the whole life-cycle cost of an asset. Let's say it's a road and it would be built to last for 40 years. The government is fully aware of what the costs are over 40 years and contracts out the maintenance of that asset over time.
What we see with traditional procurement is that sometimes the decisions are made more on the basis of short-term costs, actually building the road, and with less awareness of the cost of maintaining this asset over the long term. So sometimes, 10 to 15 years down the road, if finances are a bit tight, governments may decide to limit their expenditures on maintenance, and this can lead to the deterioration of the asset.