Well, you are very right, but is also interesting to know that even without using VPN, Many of us still encounter the free roll error which sometimes say that someone else have used the same IP to claim as we..
But all the same, it is still very advisable not to use free VPN since that could make the whole matter worst, and also using free VPN to play on several other casinos may result in the system flagging your account for multi accounting which could trigger KYC request from the casino.
Other reasons why you might get the some else has already played message could be on a mobile phone connection you get a different IP each time you connect and the last person to use that address might also use freebitco.in. That's quite common in uncertain countries with a limited choice of mobile providers. I'm not 100% sure whether is becoming an issue or not but Cloudflare doesn't use IPv6 so if you have an ISP that gives you a IPv6 address then Cloudflare converts it to a IPv4 address. I suspect that could cause the same problem.
We don't KYC people for using VPNs.
It's true, if you need to use a VPN for gambling at one casino it's always better to avoid free VPN because many people are using them and you are the most likely to encounter issues like multi account flagging with them, especially if you had some good winnings. I think casinos are aware that these IP addresses are VPN addresses actually, but they let people play with them instead of blocking them for unknown reasons.
Are you using a paid VPN personally? Which one is it? IMO even paid VPNs can cause problems if they are largely used.
I can't speak for why other casinos do what they do but we don't block VPNs because lots of gamblers value their privacy. Using a VPN to gamble shouldn't be any reason to get flagged.
With us being a faucet as well as a casino we obviously get a lot of attention from multi-accounting abusers. They tend to use a certain selection of VPNs which are most suitable for their purposes. I used to try blocking just those VPNs but the problem is that they just switch to another provider and I ended up forever one step behind in blacklisting them.
I've come up with far more sophisticated ways of catching them but the most important is shadow banning so they don't know what exactly they did to get caught.