Crypto is a growing industry, there will definitely be scammers trying to take advantage of it and use it to rip people off. This is not limited to just crypto, scammers use and have used any available opportunity they have, it's a media narrative to paint Bitcoin as the top tool for scams.
Scammers are in all industries, not only in blockchain and cryptocurrency industry. If people are scammed in cryptocurrency, they can be scammed in other industries too because they have personal traits that can be abused by scammers. Too naive, too greed, too careless, all these things, but even more, are perfect traits for scammers to succeed.
This is not particularly true. I've personally engaged with a couple of clients and potential clients who were aware of my nationality and experienced no prejudice from them. With how popular Nigerians are on social media, you can be sure there are lots of others who are not limited by prejudice, if they create a track of being upright and trustworthy.
There are good and bad people in a same local area, a same country, but education and culture actually affect locals a lot. If you are a Nigerian, it does not automatically mean you are a bad person. There are bad people everywhere on earth but if you are from a nation that is famous with scammers, you will have to put more effort to prove that you are a good person.