Buying, or investing in, existing companies and then using his marketing skills to convince other investors (and governments) to pour billions of dollars into them is hardly the same thing as "building rockets that land themselves" - you can thank the engineers and visionaries at SpaceX for that. And his cars absolutely
do not drive themselves despite his constant reassurances that they'll be able to do so Real Soon Now™.
In fact, as an aside, I would argue that Tesla's marketing is disgustingly misleading - their website loudly proclaims that all Teslas are equipped with every piece of hardware necessary for fully autonomous self-driving, and in a much smaller, much quieter voice they subtly admit that none of their cars are capable of actually doing that yet.
You may handwave that away as marketing fluff, but if you asked the average person in the street whether Teslas can drive themselves, 90% of them would say yes, of course they can, when in reality they're merely on par with other makes and models that have had the exact same driver assist features for years.
It's misleading at best, and lethal at worst - lives have been lost because drivers blindly placed their faith in autonomous driving features that simply do not work as implied. Go ahead and chalk that up to the drivers not being attentive enough, of course they share the bulk of the blame for not being in control of the vehicle they're driving, but it's hardly a surprise that many Tesla drivers have been lulled into a false sense of security by Tesla's marketing.
But again, nobody is arguing that Musk is running a straight up scam or that the products don't exist, the criticism is that he is constantly making promises and predictions he can't fulfil, constantly making claims that sound impressive until you look beneath the veneer, and whenever he is challenged to back up his assertions he either messily dodges the question or launches into yet another Twitter rant, and all the while his fans eagerly accept whatever he says without any care for objective reality.