Headless e-commerce has been growing lately. See the MACH Alliance [1] to find out about closed-source platforms in this space. One thing to note is that we can see more and more specialization, new categories, such as headless loyalty/PIM/search etc., appeared on the market. Earlier this year, I wrote a short article [2] explaining what problems these APIs try to solve (sorry for the clickbait title).
[1] https://www.machalliance.com/members
[2] https://dev.to/voucherify/whats-mach-and-how-it-can-make-you...