The problem is that those DLL files from Firebird need the C/C++ runtime from Microsoft. These are often already installed by other software but on a clean fresh Windows system they are not installed and in that case the Firebird DLLs only work after installing that C/C++ runtime.
SQLite also requires MSVC.
SQLite also requires ICU to support more than just ASCII. Although those are internationalized forks, like SQLite3MC. Official SQLite library only support ASCII and doesn't support anything outside basic Latin.
So this is not the problem. The problem is in everything else - dozens of additional files, like conf, msg, plugins, intls. Older embedded was just a single dll file.