Runescape has been that game wherein most people are just grinding for the money, and it's nothing really new to meet people who are selling and buying cryptocurrencies. They will add you on Discord groups to facilitate the transaction before the trade happens, and they don't really ask for much information as long as you have the money/in-currency and that's pretty much about it. Kinda like P2P trades happening on crypto though this time you don't trade real money but rather in-game currency, and the devs of the game don't really bother much about it.
Runescape was actually the first online MMORPG i played. Discovered it and started playing back in 2003. Still have access to my account and I do login like 4/5 times a year just for the nostalgia. Yeah, it isn't the same like it used to be.
But, the way you are saying, it sounds like everyone playing the game sells their rsgp (money) for cryptocurrencies which isn't true. You won't randomly meet people who are selling/buying cryptocurrencies for items or rsgps. It is against the rule to do real world trading. Those who illegally sell rsgps through other websites or forums bots 24/7 to earn those rsgps. They usually get banned within hours and any account that has traded those bot accounts will receive a ban eventually (people even got banned after months!). Jagex mod can trace trades. I remember Jagex taking legal action against a lot of gold farmers, bots and sellers. Google "Mark and Eric Snellman vs Jagex".
devs of the game don't really bother much about it.
Wrong.