I know these sort of things happen a lot right, and I know a lot of people get stung by them. However, when you are advertising a giveaway for 5000 BTC, surely people don't actually fall for that? That's a lot of Bitcoin for early adopters let alone for someone willing to give away. This is usually from youtube accounts, and people who have zero presence within the Bitcoin community which is another huge red flag. I'm not convince that anyone actually falls for these ludicrous giveaways?
Basically some (a lot) people don't view Bitcoin as money, they think it's some shiny thingy, so their brains just don't have the same response when they encounter something fishy. Also non-bitcoin people are not used to Bitcoin amounts, so they don't immediately understand if, for example, 0.1 BTC is a lot or not. It takes conscious effort to go and check the price and do the calculation, while phrases like "$100" are immediately understood, even to those outside of the US. Plus Bitcoin is still so new and full of strange things (to outsiders), that some might things that maybe someone
is giving away a lot of coins.