What do you mean by “I don’t take it seriously”? You don’t regard Rabbi Ganzfried as a Torah scholar? If so, why not? (I simply assume that he was a Torah scholar, since his book is common in every Jewish home.)

He was a great Torah scholar, but like the Shulchan Arukh he didn’t make a point of distinguishing between recommendations, laws, Torah-level obligations, and rabbinic obligations. In his case, that’s probably because the target audience of his book was ordinary householders who wanted clear guidance and bottom-line rulings.

Praying with tefillin is Talmudic law, not a recommendation. And the source of this law is the Magen Avraham, who wasn’t writing for ordinary householders.

Could you point to a post or article where you explain why the Shulchan Arukh operated this way?

I don’t recall ever writing anything about that. What’s there to explain here?

Regarding the Kitzur Shulchan Arukh you wrote, “In his case, that’s probably because…” so I thought maybe there was some similar assumption regarding the Shulchan Arukh itself?

In the Shulchan Arukh it’s rarer. The lack of distinction between rabbinic and Torah-level law is because it isn’t dealing with punishments (which don’t exist nowadays), although there are practical differences for cases of doubt. In the Kitzur Shulchan Arukh it’s much more blatant, and customs and pious practices are included there too.

Thank you very much!

Zapta is the name of a Kutite, God forbid.