They have no products to sell, they will implode. Dumbass.
Are you speaking of the tech sector, or the finance sector? Actually, you could be speaking of both, but I think you are talking about 9 out of 10 of the top companies by market cap.
Let's list them all, and see what they sell:
1) Apple = They sell everything from Apple computers to Apple iPhones. They have access to massive amounts of information about their customers from what websites they go to, to what time they wakeup, so they sell their customers information.
2) Saudi Aramco = Not a tech company, so it really does not matter that they sell oil and a few chemical products other than oil. They are also heavily invested in other companies.
3) Microsoft = They sell software, and some cloud computing. Software may not seem like anything to you, but to customers it does seem like something.
4) Amazon = What don't they sell? What they collect is information on all those sales. On top of that, they sell fantastic cloud computing services. Basically, if you want a server, but do not want to worry about investing into the permanent infrastructure of a server, you go to Amazon. On top of the rest, they have a huge streaming service. The top three are probably overpriced, but Amazon may well be right priced.
5) Alphabet = It is basically Google. It sells the people who think they are its customers. It gives free services to people, and then sells those people attention to advertisers. It begins to be like what Matt is talking about and selling nothing concrete, and yet it makes a healthy profit doing what it does. I would like to see them pay dividends, so I would feel that profit is real.
6) Facebook = It sells it customers to advertisers too. Again, I would feel better about them if they paid a dividend.
7) TenCents = Video games in China.
8) Tesla = Cars and batteries in general. Investing in them is investing more in what they will hopefully sell in the future, than what they are selling right now. Whatever they sell in the future, I just cannot imagine it will meet all the hype... But I could be wrong.
9) Alibaba = They are in some ways like a Chinese Amazon. They lean more heavily into wholesale. We are all indirectly customers of their's. I always have the strange feeling there is a way to do what they do, but be a protocol and not a single platform. That would allow even smaller players into the international trade/manufacturing. It is one of those ideas that is just swirling at the moment.
10) TSMC = They make the computer chips in just about everything. They are so successful, it is hard to say they even have a real competitor. They do not design the chips, but they almost always manufacture them. They have been overwhelmed by orders, and there have been shortages of chips which has hurt the car industry.