Hashtags are often a combination of several words and must be constructed without spaces. Most people leave all letters of each word in lower case, something like #allaboutaccessibleinformation. For some people it takes no effort to decipher the sentence and to understand where one word ends and another begins. For others, this is not easy for a number of reasons.
Screen readers that read what's on your screen to people with a visual impairment have trouble with words being stuck together. To make sure they recognize the phrase in the hashtag, it's important to capitalize the first letter of each word. The screen reader then sees it as separate words and reads it that way. An accessible hashtag would then become, for example, #AllAboutAccessibleInformation #YouAreDoingGood #MakeYourHashtagAccessible