Why say "〜、皆には出来る。" instead of " 〜、皆は出来る。" in this context?

Question

The sentence in a translation:

将来を見据えながら点と点を結ぶということなど、皆にはできません。
While looking at the future, one cannot see how to connect the dots.

My assumption is that the following is the "base" sentence. Then, to add meaning, a に is placed before the は. Maybe it adds emphasis (or something)?

将来を見据えながら点と点を結ぶということなど、皆はできません。

I don't think I've ever seen a は and then have a に placed behind it to add meaning.

However, if the "base" sentence should be thought of as:

将来を見据えながら点と点を結ぶということなど、皆にできません。

Then I am ok with regard to particles. Placing a は after a に seems pretty common.

Answer 1

The に form is the "base" sentence here, and the は is added for emphasis.

One key to understanding how できる happens grammatically is that できる is often describing the thing that can be done, instead of the people or things doing the thing. Sometimes a closer gloss is doable rather than can -- English can describes the people or things doing the thing, while doable describes the thing that can be done.

In your sample sentence, the topic is こと, and all the stuff to the left of こと tells us what kind of こと it is. The できません applies to this こと -- this こと is not doable -- and the 皆に here tells us who or what this こと is not doable by.

Addendum

The grammar for できる is at least partially attributable to the historical development of the term. See this other post for details.

Answer 2

Reason for using「は」

The「は」provides contrast. It provides an unspoken (in English) and contrasting parenthetical context as shown below.

日本語の読み書きは皆にはできません。

• Not everyone can read and write Japanese (but some people can)
• Not just anyone can read and write Japanese (but many people can)
• Not all of (you) can read and write Japanese (but some of you can)
• Not all of (them) can read and write Japanese (but some of them can)

Reason for using「に」

The reason for this is that できる is describing the "possession" or "existence" of a capability to do something.

日本語の読み書きは皆にできません。

So just as you would say,

「野菜は冷蔵庫にあるよ」or「コーヒーはキッチンにはないよ」

to describe the existence of things at a location,
you also use the same construction to talk about the existence of ability in a person.

「あなたにはできる」 or 「わたしにはできない」

Taking a cue from Eiríkr Útlendi's answer, you could think of the に here as marking an ability possessed by a person.