some_collection.where(x -> x.name == 'foo').sort_by(x -> x.age)

These functions are tiny and trivial. They don't need names, and if you were to give them names, the extra weight becomes burdensome. Not just in syntax duplication, but the redundancy of the name as a comment on the trivial function body.

    nameIsFoo = x -> x.name == 'foo'
    getAge = x -> x.age
    some_collection.where(nameIsFoo).sort_by(getAge)

Note that giving the functions names has also changed the source order of the function bodies. Now you need to do a mental cross-reference to follow, instead of being able to read the definitions inline.