First, if you are exclusively (or primarily) applying through online applications I'd strong suggest you reconsider your search strategy. That strategy is not n

First, if you are exclusively (or primarily) applying through online applications I'd strong suggest you reconsider your search strategy. That strategy is not nearly as effective as getting in through a side door - the front door is crowded, and the bottleneck tends to get most candidates ignored. These online applications, with some exceptions, are usually the resumes that get only a few seconds to make an impact - you might lose your reader in the first few sentences (note: I haven't worked in big company recruiting from an internal role, but this is pretty widely acknowledged and studies have been released confirming how little time is given to a resume in these conditions). Why do some companies not accept cover letters? For one, nobody wants to read them. Keep in mind, nobody wants to read cover letters OR resumes. They want to have a conversation, and they want to be able to determine as quickly and accurately as possible whether or not that conversation is worth having. This can be quite prone to bias. Most cover letters simply reiterate what the resume says, but in a condensed format, along with some fluff about how hard they work and how strong their soft skills are. It's usually fairly pointless, and some companies ask for them as a bit of a test of your interest. Companies that don't ask for them likely don't feel they are useful, and would rather have their recruiters looking at resumes (and hopefully actually having conversations) than reading traditional formatted letters.