What people call “demonetized” on YouTube is actually called “no or limited ads” inside of YouTube Studio. It’s not Google but the advertisers who don’t want their Coca-Cola ads shown on those videos. YouTube Premium views still pay out on those videos since they’re not ad views.
If everyone paid for YouTube Premium and didn’t use the ad-supported product, then advertiser boycotts would have no power.
It’s not that they got DDoSed, it’s that unregulated off-shore gambling is illegal in many countries, so their IP addresses were getting blocked in these countries. The way CDNs like CloudFlare work is that many customers share the IP addresses, so they were getting other CloudFlare customers blocked as well.
CF wanted them to move to a “bring your own IP” plan so that their IP blocks wouldn’t affect other customers, and that came with the steep price tag.