It's not that twitter is not doing anything , but that scamming people out of crpyo currency and money is very lucrative owing to human gullibility and the viralness of the twitter platform, so scammers have an incentive to keep finding loopholes after twitter closes existing ones. And most scmamers fail to bypass twitter security measures, so all you're seeing the ones who succeeded. if 90 scammer fail and 10 find a loophole, then those 10 will proliferate until twitter fixes it again. It's sorta like a virus that acquires drug persistence.