Company valuations aren't a sum of the cash flows invested into a company or the available cash flows out of liquidating it either. These aren't uncorrelated numbers but you can technically get a six trillion dollar "valuation" from one person paying $1 for a sixth of a trillionth of a company.
It would be really interesting to get a snapshot of the actual dollars spent on ownership at any one point in time. Stock market volume can be a lot of froth and slosh of a small-ish subset of all shares.
No they aren't, but it is an example of relative scale of investment. Especially when much of that market cap growth has come just within the last 5-6 years or so. Money could have flowed to other ponds collecting off the river of investor cash flow instead of this one massive lake. This might have lead to a different growth trajectory in our economy and technological development than one so focused on the ROI of chip production in particular, to the exclusion of much else. The fact that much of that demand is brought up by circular investment is another aspect. Two lakes backfeeding into eachother eating more and more of the flow off cash flow river, drying up other ponds along the way. Much is lost with such unitary focus of investment.