I've been in this space for 15+ years now, worked with most of the main players that have on-prem and SaaS solutions, and deployed and run solutions at scale at a few of the largest companies in BigCo land for multiple years now.
I would be cautious on focusing too heavily on the 'developer as the customer' here. Most buying decisions in this space are not made by IT, they are made by CMOs, CXOs, CDOs, etc as that is who owns the budget (and results) tied to this type of solution.
At almost any scale, when you look at total cost of ownership, licensing from one of the main solution providers is usually quite a bit cheaper than building out a whole proprietary stack that one then has to maintain in house via their IT org that likely is not an expert at this kind of stuff.