For example in beverages and fashion the capital needed for production is very limited, it's all about marketing and getting marketshare. Software is a mix where building is not as trivial, but it's for those big companies mostly about positioning and sales. Those industries are much more sensitive about ROI, it's not easy to find ways to spend you money in those areas.
Google/Apple/Facebook are just very profitable companies with in internal investment arm because they don't pay dividends or make huge buybacks, what a traditional company like CocaCola would do with those huge profits.
There are investment companies with hundreds of billions under management, so that's also nothing out of the ordinary. So the money is still invested, those companies don't have their billions on a bank account. Only this way those companies still have access and control over it, for acquisitions for example. Is that a good thing? Probably better than in some random fund owned by some individuals who are much more risk averse.
Tesla is another story, but from an outside perspective it's just very risky. They could've easily went bust if the Model 3 production went south, that's why it's tough for him to raise capital. Not many entities can gamble like that with billions, if it was a sure deal there would easily be enough capital available for Tesla. Look at the balance sheets of mayor car companies, for example Daimler has a quarter of a trillion in assets.