I think there's probably a few things here that are worth a comment:

- Information imbalance: from people I've talked to in decently senior roles at even very large companies, it might be surprising to learn that information can be poor at every level, because generally the people who are responsible for hiring at even fairly senior levels are not directly also responsible for expenditure, especially when macro-economic conditions are responsible for those financial decision. Essentially, the person who is responsible for setting the hiring targets to enable 20% growth is likely not responsible for modelling what happens if the cost of short term debt goes from 2% to 10%. Probably this is most likely in the superscalers, and it's likely hardest in the companies from 2-5k people - with a tech org of about 1k, you're likely acutely aware of the impact hiring strong people can have on your product while lacking the numbers to approach the problem analytically and with a sophisticated finance org. Basically, the number of people who could reasonably be expected to consider 'if we hire too many people, we'll have to fire them' as a significant part of their brief is smaller than you might think.

- 'There's no physical machine the company is adding that allows the workers to do their job which they couldn't themselves easily acquire'. Ignoring the focus on the physical machine bit and focusing more on the creative part of 'what does the company add, what do the people add', your claim may be true in some parts of industry and if you're in that side of industry I lament your situation, but for large parts of industry it's unequivocally false. There's a huge amount of value add that the machinery of an engineering organisation adds. In the more creative spaces, anyone who's operated in a truly high performing culture will have observed that a lot of the culture of building comes from the grouping of people who've been very, very carefully hired for, who've been carefully placed on team together, where memetic techniques have been used to proliferate certain positive behaviours, raising people up. We succeed as a team and fail as a team. You can see this over and over in so many testimonials - the stories from those who worked at Xerox PARC, stories from the MIT LISP hackers, back 50 years, all the way through hearing about the work the M1 team was doing, seeing the companies that spawn hundreds of startups from their alumni. And that's not to talk about the companies who specifically use process and ritual to ensure that engineers are consistently at the bar across massive orgs, from Google's exacting bars for code quality all the way to the consulting arms of Oracle, CapGemini etc who can approach repeated problems and get the most out of their engineers in a space where it's arguably harder to hire talent. And this is totally forgetting the huge non-SWE parts of orgs required to enable success - sales, finance, marketing, etc etc.

- Tech workers are still underpaid - think there'll be a rude awakening coming for you I guess. People across the world get paid based on how much they can get in the market (and if you're already at the company, the switching cost). There's room for places that do it differently, but not much room. If a large number of qualified people join the labour pool, you can bet that the practical market comp goes down.

- Paper losses are not true losses and you can just wait for the price to go back up: Honestly, that's wrong on like every level. Firstly, at the company level, there's a very real risk for many of these companies that they go bankrupt. Spotify has something like $2.8B in cash equivalents, has revenue of $9B and expenditure of about $9B. If their revenue dips by 20% due to e.g. a global recession, that cash supply will last them about 18 months. Before they get there, they have to raise more money. If raising via equity, they're going to be raising at their new and lower valuation, so their investors take a huge haircut. If they raise via debt, they'll be getting charged a lot on interest (because their risk of default is nontrivial). My brief but non-zero insider knowledge of some of these debt deals make it very much sound like a sellers market. A smaller company might expect to see 15% interest demanded - if you need $150M, you're in trouble. The staff who Spotify are dropping today likely represent $300M over that same 18 month period. You can bet that they'll be making this cut after scraping the barrel everywhere else.

Now, for the actual investors - if you take a massive paper loss, you're basically not getting that money back on a reasonable timeframe. https://danluu.com/norstad/risk-time/ is a good article on this topic. The simple way to think about it is that if in the good years you get 4% a year ROI across your portfolio and then you take a 50% haircut once, it will take you 18 years to make that difference back. The people who invest in tech companies are in large part not rich billionaires looking to pay for their next yacht - they're institutional investors, mutuals, pension funds who are looking to maximise returns for their members.