Because most of the people who post/write these articles do not actually know the C language specification nor understand its design.

Understanding three important concepts properly in C allows one to easily identify what can/cannot result in UB viz. 1) Expressions 2) Statements 3) Sequence Points and "Single Update Rule". It is not that hard at all.

I wrote about it here with links to further reading provided - https://news.ycombinator.com/item?id=48144734