But they did. All 7 million of them - that’s why their data was visible for those 14000.

As it says in the article:

From these 14,000 initial victims, however, the hackers were able to then access the personal data of the other 6.9 million victims because they had opted-in to 23andMe’s DNA Relatives feature. This optional feature allows customers to automatically share some of their data with people who are considered their relatives on the platform.

Here’s what each and every one of those 7 million people opted in and agreed to:

https://customercare.23andme.com/hc/en-us/articles/115004659068-DNA-Relatives-The-Genetic-Relative-Basics