I forgot to cover this a few weeks ago, but we have new thresholds in place since January 1st:
Works: €5,225,000 (was €5,186,000)
Central services and supplies: €135,000 (was €134,000)
Sub-central services and supplies: €209,000 (was €207,000)
Utilities and defence: €418,00 (was €414,000)
Why do thresholds change every two years? Because that is the commitment the EU made in the context of the revised Government Procurement Agreement, where for third country access to the EU procurement market the thresholds are expressed in Special Drawing Rights.
As for why they exist and their current level, there is still no explanation other than these reflect the commitments the EU made for the GPA. I have a paper on this topic coming out in the very near future, but here's an older one about thresholds.
In the UK they have fallen slightly from previous levels but only due to the changes in the the GBP-EU exchange rate.