What does either of them have to gain by saying Bitcoin and other cryptos are a sham?
It is a strategy, which will, I don't know make them more richer..? Isn't it funny when Bill Gates say crap bitcoin while Microsoft is working on their own blockchain technology

Nah, I think they believe it. Actually I wasn't aware that Gates thought this way, but I certainly knew about Buffett--and they're both entitled to their opinion. It makes sense that WB doesn't think bitcoin is a good investment, as he's a stock market guy and doesn't see what problems bitcoin solves. You'd think Gates might be a little more sympathetic, being a computer guy, but whatever.
I don't believe there's any sort of conspiracy here. I think they got asked by the media what their opinions are on crypto, and they stated what they believe. I have great respect for both men, and their opinions don't diminish that in the least.