The following is to address the question "why" in the OP. Some contemporary positions are already brought in another answer.
There are three concepts involved:
(a) reading, even looking at, mundane writings, etc. in Shabbos - a Rabbinic prohibition based on the concern that you might correct them.
(b) a prohibition on learning secular subjects in general - which where/if prohibited, is prohibited during the week as well.
(c) muktza - the writings, books, documents etc., forbidden in this way become muktza in Shabbos.
And, there is a leniency that not everyone follows:
(d) books of wisdon, knowledge, medicine - some say you can read them in Shabbos, which implies that you can read them during the week.
These are the essential concepts. The Shulkan Aruch elaborates on lists in shul, personal guest lists, menus, attending theaters (mushav letzim), assembling your telescope, greetings, letters from outside the tehum, history books that a person might read to learn the language, and so forth.
Notably, your question about enjoying the news is in the Shulkan Aurch, too.
Shulchan Aruch Harav, 307:21-31, which is now available in English, provides an especially clear exposition of the foundational concepts and examples.