Actually on servers RHEL is still the default (43% server OS market share), followed by Ubuntu at 34%, Debian at 16% and SuSE at 11%.
https://commandlinux.com/statistics/linux-server-market-shar...
Enterprises love RHEL because of the paid support, even if they never use it, it's "there".
They're talking about billions of dollars of market share, so how does debian get a mention being free? I'm suspicious of their methodology.
At least the infographics down the bottom are obviously full of slop