Because they're not paying only for Wordpress-the-software, they're paying for scalability, maintenance, etc. $100k/mo is probably cheaper than a team of high-end WP experts.
Same reason a ton of us pay for AWS/GCloud/Azure instead of dealing with bare metal. (And I say this as someone running an edge fleet. If I didn't need to, I wouldn't.)
News sites can be very large - so running on Wordpress.com infrastructure can cause such amount. With cloud storage (provided by WP), additional support etc.
