- It's easy to find case studies to help explain and plan your project.
- It's easy to find vendors who can build or support the technology. That makes it easier to run competitive RFPs, and fire/replace vendors without having to rebuild from scratch.
- You benefit from a security program that has a lot of inputs--a lot of bad guys trying to get in, and a lot of good guys trying to keep them out. The code is battle-tested and frequently patched.
- You benefit from a community module system that has a lot of inputs. Chances are if you want to do something, there is a module to do it, or at least get close.
- You can more easily empower "tech savvy" employees to do pseudo-development tasks like build filtered lists and manage content workflows. It's easier and cheaper to scale tech-savvy employees than full developers.
- There are enterprise-savvy support options available.
- It's easy to find hosting.
Developers, particularly those who want to innovate and build new tools and products, tend not to value these sorts of things as much.
I mean, there are downsides to SharePoint: it's commercial software and there's more friction than with Drupal. But I'm not even sure how relevant that is anymore in today's IaaS hosted world -- I can go on Azure and deploy a Sharepoint server in 5 minutes from an image and the licensing costs are baked in.
But you're right about developers not valuing these -- CMSes are for established businesses that need a technology platform to manage their messaging across multiple channels. If you consider yourself a product hacker, then something like a CMS isn't likely to be interesting to you.
You're not going to get an accurate picture of the CMS market here on HN. Most folks here are developers...PHP CMS's are not what they are interested in. The prevailing opinion on HN is something like "CMS's suck, you should build it yourself with node/React" or whatever.
If you need to build a content website, and the information architecture is complex, Drupal is a very strong choice. I haven't use D8 yet, and I would not recommend building a high-profile project on it yet, unless you really want to be an early adopter. But D7 works well and will be supported for a long time yet to come.
If your info architecture is fairly simple, take a look at Wordpress. You'll have an easier time finding low-cost vendors than with Drupal. Drupal is powerful but expensive.