In Spring Framework 6.1 we added a number of improvements to data binding via constructor args such as DataBinder support for constructor binding (#26721) including nested constructors (#20806), customizing request parameter names for constructor binding (#30947), and declarative binding mode (#30948).

This makes constructor data binding a safer alternative to setter binding because it's selective about what we bind from, but to make it more complete, it needs to support collection and map arguments.