What are the best reasons for a new project to choose Drupal in 2026, apart from familiarity ?

I'm partial to Drupal because I use it a lot - but if you have a large team with a lot of rules around content and making a mistake is a big deal - you don't want to re-invent the wheel with CMS-like functionality.

Remember a while back when the world first heard about Mythos because there was a mismatch between what the "CMS" said was publish, what was shown on the site, and what was "really" available? Those types of problems haven't gone away and if anything are more critical when an army of agents will seek out and find any but of information they can get their hands on.

Not a best reason, but the reason is often because, in the enterprise, marketing hired dozens of people between 2018 and 2023 from the same handful of Drupal consultancies.