Some are in it for "glory" or "kudos" - some simply are in it because they were on the "fan side" once and know how much it means to people. There are those that have their own agenda sometimes, intentionally leaking something they know the fan base will get riled up about in an attempt to induce them to make enough noise to prompt TPTB to make changes. There are many, many reasons (and I'd think most people have some combination of them). I think most of them are on the "up and up" and wouldn't actually leak anything that could be damaging to the company, simply informational.
Given how simple it is to get info out there in a sophisticated enough manner it's really not a "danger" to most folks, generally. The folks that do it smart either funnel information through others they trust, time things so they don't clash (you don't post something the day you get told it, for example), or they don't make 'personal' posts with the same handle/username/etc. For instance, if you posted an "insider info" post and then mention that you have to go feed your dog Spot and go pick up your girlfriend who works at the MK ticket booth, LOL, you are cruising for a bruising (if it's true and not misdirection).
From my understanding here, the reason Disney has gotten so irritable this time is because a) Star Wars (biggest thing like ever) and b) the person(s) who made some recent leaks were way too overzealous and inexperienced, revealing more about themselves/sources than would have been advisable. It's slightly understandable as this is the topic of the decade, if not the century, when it comes to WDW - and theme parks overall - but that's the time that in retrospect, more caution should have been taken versus less due to the excitement.
