The reason so many scams are improbabl is that they're deliberately weeding out people who are more discerning. For anything where an actual person has to engage you from there end, the process is about fishing / filtering it down to the few people who will be susceptible to manipulation. Hence why when you hear about these scams they sound so unbelievable. It's that very unbelievableness that makes them successful.
Their goal is to maximize the amount of money gained per scammer-man-hour, so they want the absolutely most gullible people on the planet. The supply of gullible people exceeds the amount of scammers, so they spew a zillion spam emails but they only want to actually hear back from a few of them. You
can actually help by completely wasting their time, in other words. See this one for some fun:
https://www.youtube.com/watch?v=N682eopajzAAs for Vin Diesel Lady, I think we can go a bit more nuanced than "dumb". My guess is that she has problems with large numbers in general, such as working out the scale of things or relative probabilities. 7 billion people on the planet and Vin Diesel DM'd her, specifically. Then, Vin Diesel needed some of her measly dollars to fix his movie gear. Someone DM'd you and said they're Vin Diesel, which is an unlikely event, but how unlikely an event compared to being DM'd by the actual Vin Diesel? Actually, much more likely but you need to be able to do the rough estimate in your head to work that out, and some people don't have the cognitive framework for working this stuff out. And for the money part you can realize that movies cost a
lot of money to make, compared to the amount of money any average person has, and she clearly wasn't able to realize that as a red flag either.