Why should they? i dont understand this weird obsession people have with characters never making mistakes or making stupid decisions; even when said character has been shown as pretty terrible to begin with .
Good writing is writing consistent characters and compelling scenarios for these characters to interact within. Characters making stupid choices is NOT "bad writing" by any stretch of the imagination.
It's funny how the internet has given such a vehicle to armchair english scholars to pretend like dumb characters shouldn't exist in fiction.
Andrea hasn't been presented as "dumb." She is presented as a very capable character with a strong tactical mind. It is her personal judgment that is questionable, particularly in dealing with men like Shane and the Governor. Many of the things that would be attributed to her being "dumb" are just poor fucking writing, because the writers don't know how to set up situations without having characters act very illogically. We've seen this repeatedly with this show.
In any case, the reason it was bad writing is that it was not a decision made by Andrea. For it to be a decision made by her, it would need to be addressed on screen. This could have been accomplished with a two second scene, while she's walking out of the building into the woods, if they showed her look at the truck, think for a second, and decide to move on. Then, when the governor caught up to her later on, it could have tied back to her failure to decide to take or sabotage the truck. That would have been decent writing.
Instead, they ignored the truck completely. Why? Because it was a device needed for the Governor to catch up to her later. Rather than deal with it, they just ignored and hoped no one would notice. Everyone noticed, because it was glaring. That's bad, lazy writing.
I don't understand why people are so willing to make excuses for bad writing just because they enjoy something. I enjoy The Walking Dead. I can still recognize this as a flaw.