Because of eyeballs and attention. Creating a brand new site and posting on it in this day and age is basically the equivalent of yelling into the void. No one is going to see it, and the only way to get it to come up on Google is by typing in "site:[myblog.com]), barring the few friends and family members who may give you a pity click when you post on your social media.
Almost nobody is writing anything 'just because'. They're writing because they want to be noticed, either as a "domain expert" or "thought leader", or simply as a stepping stone to a writing gig at HuffPo, Forbes.com, Inc.com, whatever replaced Gawker and the various pipelines of formulaic listicle generators out there that might pay a few pennies for the next "Elon Musk's top 10 secrets for Productivity" gruel.
Almost nobody is writing anything 'just because'. They're writing because they want to be noticed, either as a "domain expert" or "thought leader", or simply as a stepping stone to a writing gig at HuffPo, Forbes.com, Inc.com, whatever replaced Gawker and the various pipelines of formulaic listicle generators out there that might pay a few pennies for the next "Elon Musk's top 10 secrets for Productivity" gruel.