I would take the perspective of the gamblers in this situation. Are there any rules protecting them and their wagers?
Going through the ToS of so many gambling sites, they put in lots of leeway and wiggle room which allows them to legally protect themselves should a flaw in their system be exploited. So when such flaws are brought to light, mostly when a big win happens, they reserve the right to refuse to pay the player.
We should also consider that many players may have unintentionally played games that would have been otherwise rejected were they to have hit a huge winning due to there being a flaw, but as they didn't, there was no issue and their stakes were lost, so they were always going to lose either way.

Taking advantage of a obvious system error is no doubt unethical, but does it qualify as scamming, I don't think so, as intention cannot be judged easily.
• If I visited an ATM and it dispensed more cash that I requested and I kept the money without counting it, that should not be a scam as I wasn't aware and not in the habit of counting cash I receive from a machine.
• If I indeed counted it and still kept the money (thinking; my lucky day), this is open to discussion, but possibly an exploit.
• But if I counted it, kept the money and attempted several other times to cheat the machine, this should be outrightly fraudulent as I'm taking advantage of an obvious glitch repeatedly with intent to cheat. A scam.

Intent is important both on the part of the platform and the gambler.
• If the same machine were to be underpaying people who use it and the providers were aware but left it as most were not aware, up until a scammer comes along and exploits that flaw to their advantage, and at this point they whip out their user agreements. Have they been running a scam?