Every single language I've seen that has been 'loved on HN as "taking over the world"' has had C FFI interop, whether it is Node, Rust, Python, Ruby, C#, Java, Haskell, Zig, Crystal, Julia, LUA, etc.
Web assembly is the browser C FFI, not some high level platform like Java or .Net. Your examples aren't comparable.
Failure to understand what bytecode based execution runtimes is all about it seems.
Also failure to understand that C ABI does not exist, rather it is the OS ABI from OS written in C, and that other OS, not written in C, don't have such thing as C ABI across all languages.
Examples of such OSes, IBM i, z/OS, Unisys ClearPath, UCSD, Unisys ClearPath, Classic Mac OS, UCSD, Native Oberon, Mesa/Cedar, Windows (plenty of stuff is .NET/COM/UWP nowadays), Android, ChromeOS, Garmin OS, and the Web.
So no, it isn't the browser C FFI, all major ones aren't even written in C for the past 20 years.
You have repeatedly missed the point of the discussion because you are hyper-focused on the implementation details that are irrelevant to the end user. I honestly don't know how you jumped from the JVM and CLR to Unisys Clearpath (twice) and Mesa/Cedar except as a red herring. The topic of discussion is Web Assembly which implies a modern browser.
The majority of browsers now support Web Assembly and about half the global population has a web browser and access to the internet - and now, access to an actual universal bytecode based execution runtime by nature of being part of the web browser standards instead of an OS feature or framework installation or (god forbid) Oracle TOS.
The C FFI part was an analogy. The whole point of Web Assembly is that it can't call out to just any library on the OS.
Except it can, because WebAssembly has long stop being a browser only story.
By the way, JVM on the browser, Flash CrossBridge and PNaCL were there first in what concerns "universal bytecode based execution runtime by nature of being part of the web browser".
Web assembly is the browser C FFI, not some high level platform like Java or .Net. Your examples aren't comparable.