Why is ensquare not a word when encircle is ?

Geometrical discrimination

The prefix "en" comes from Latin and only goes on words, such as "circle", that are similarly derived. "Square" comes from Greek and can only be modified by appropriate Greek prefixes.

Best answer? (Even if it is all just made-up?

Because circling something is not a comparable action to squaring something.

the ensuing process to think .... enclosed took it covered the square

I am not ensure.