The Prussians wanted a Prussian-dominated Imperial Germany - and they wanted it to come from the top. All the rulers of Germany - counts, dukes, princes and kings were to voluntarily submit to the Emperor in order for the state to be legitimate.

It was Prussia that took Alsace-Lorraine from France, not Germany.

The German-speaking cantons of Switzerland had no desire to join Germany and no high nobility or rulers that could do it for them. Since the cantons did not vote to join. Germany did not want them.

Note that there were plenty of Germans in Bohemia, Moravia and Austria that were not asked to join, since their ruler, the Austrian Emperor Franz Joseph did not want to join.