Tech support forums hosted by a large company are nearly impossible to be useful. They run them because someone has the good intentioned idea that a lot of people have the same questions, and seeing other people asking and answering the questions could help people solve their problems faster. Also, some people just want to be helpful, so maybe some customers could help other customers.
The problems are many:
a) to be completely honest, many users experiencing problems aren't willing (or able) to read already written messages about their problems. Even when the error message tells them exactly what is wrong and how to fix it, even when the FAQ tells them exactly what is wrong and how to fix it, even when there's a forum post that tells them exactly what is wrong and how to fix it that's suggested when they write their post, they'll still post their same question; or if you have a real live support person, they'll send it in to them.
b) forums are amazingly time consuming to moderate. If you don't let posts go live by default, people will complain about censorship and how terrible it is and write the same post multiple times because they thought it didn't go anywhere. If you do let posts go live by default, people will use your forum to be terrible people and share malware and music and many worse things.
c) As your product changes, many, but not all, old forum posts will become outdated and worse than useless. If you keep everything up forever, it becomes less than helpful. If you throw everything away after some fixed period, you lose out on some information that is still current; and people will waste your time decrying your censorship. If you put a big watermark up on old posts, nobody notices it. If you have someone go through and curate the information, that's a lot of effort.
So, IMHO, a forum costs a lot of effort, and doesn't make a meaningful dent in the support load. Often someone had a nice idea to run the forums, but they couldn't get them staffed for more than 3-6 months, but nobody wants to be the person to kill the forum, so they live on as a ghost town.
It's more effective, again IMHO, to automate the hell out of the support queue, but still have people reading as many requests as possible (even if it's mostly skimming and sending appropriate canned responses), with a path to actual responses as needed. The people running the support queue need to have the ability to influence the product to make their jobs easier. That means a) being able to escalate issues so that common issues are fixed in the product, b) being empowered to fix public documentation (including canned responses) so the wonderful people who read documentation have the right information, c) being able to either directly fix or escalate to have account issues fixed.
Of course, Microsoft and Google tend to be more of a take it or leave it kind of product. I don't expect support from either of them. For Apple, if you want support, you have to go to a store, for the most part; which isn't going to solve complex issues. Limiting your interactions with companies that are too big to care is the best you can do. On the other hand, the cable company and the phone company will come out and fix your lines, eventually, if you bug them enough; they're pretty big and don't really care, but they do have a smattering of support.