RE: EU Courts13 Jun 2019 15:49
Arbitration is more likely to be successful, esp. as no appeals vs a regular court action, but even so it's largely about the enforcement of a decision.
So a CJ EU judgement against Slovenian authorities would have to be accompanied by a truly painful fine, and be actually taken away from Slovenian remittances (right word?) from the EU budget.
Arbitration is faster and has no appeal, but it's based on a contract between the two parties who agreed to resolve their dispute under the arbitration procedures. Slovenia ignoring an arbitration decision would mean a breach of contract under whichever set of laws the arbitration has been agreed to be under, which itself would need proper enforcement.
Additionally, as notmanymorebrick said, many EU rules are ignored by some Member States because the punishment and/or the enforcement (or lack thereof) still make it worth their while ignoring those rules.
Hence, purely IMO, Slovenia does not seem worried about the threat of getting sued under EU law. And why I suspect Ascent has not obtained litigation finance - probably no lender saw the point in funding a lawsuit that had less than average chances of leading to damages that would actually get paid into Ascent's coffers.