I've noticed that today lots of publications, such as textbook, newspapers, magazines, etc, often don't use the indefinite articles "a", "an" with indefinite singular and countable nouns especially in adverbial phrases and clauses. I don't see any consistency in the use along with a strict following of a grammar rule - every countable singular noun should be preceded by an article (with exceptions).
Examples from media:
The CDC came under scrutiny last year
...delaying life events like marriage, having a child, buying a home, or starting a business...
...prospective students put cost at the top of their priority list.
The University of Oslo says Friday July 17, 2015, convicted mass killer Anders Behring Breivik has been admitted to...
...as O'Malley, a former Maryland governor, was interviewed on stage.
... and she was taken to county jail.
Buckingham Palace voiced disappointment after...
All the aforementioned nouns in bold can be used as plurals, which means they need an article when singular.
Please help understand.