To a certain degree, this is understandable. It may be that people are looking for ways to have a character fit the AP, not just neutralize challenges - like making sure they've got good favored enemies/terrains for Rangers, or making sure the adventure will be a good fit for paladins (compare and contrast Skull and Shackles with Wrath of the Righteous). That's a pretty acceptable degree.
Others, particularly when looking at organized play, want to play adventurers were they can get treasure best suited for their characters, but might not be looking for other spoilers. I've heard about people doing it for PFS and will match their characters with the treasure they might expect to obtain. I find it questionable, but it's not all that different from going to a DM and saying that you want to go adventuring for a particular item and having the DM present them with the research result.
I do think that some players take it too far, particularly if seeking an unearned advantage by relying on spoilers. But they're mainly just cheating themselves of part of the experience. If they're OK with that, even playing an adventure more than once, and they're ABLE TO DO SO WITHOUT SPOILING ANYONE ELSE'S FUN, it's a relatively benign issue.