1/ One of the hidden details in this article on Microsoft testing process is culture and politics. Over a decade ago when a bigger company bought my startup, they had to go through a similar culture/politics

2/ My company was lean/agile, with daily builds that went through a full automated unit/regression test that could release daily updates to customers. Their company was Microsofty waterfall development with a long period of manual testing as part of the release cycle.

3/ Culture change becomes political as people defend their jobs. The workers skilled at manual testing may lose their jobs in a shift to purely automated tests, as they may not have the skills necessary to build automated tests.

4/ It wasn't simply testing. Their update packages were inherently brittle, built in a way that was likely to fail. They were unwilling to make the architectural changes necessary to avoid the brittleness.

5/ They were therefore convinced a long period of manual testing was needed and it took years to move them off that principle.