If it really is a bad idea, and those firms have been so successful for so long not because of it but in spite of it, then it seems like a huge opportunity for others to come along and displace them with a better model. There's a lot of money in many of these tech markets. But we don't see that happening.
I guess the answer is that it's unintuitive... it seems like an obviously bad idea to many people, but the people that have the most experience think it's a great idea and continue to succeed with it.
There are other approaches: in China, for example, investors generally considered profitability much more important and expect it very rapidly, like in the first 6-18 months (though this has eased quite a bit towards a more SV-style model in recent years).
The gripe then is that companies can't have any long term vision or go big because they have to be making profit immediately and constantly.
Something about green grass...
I meant that a lot of those people are down with the land-grab now / rent later model.
It's just injection of both money and risk, amplifying the result. It'll fail more often than usual. But if it succeeds, wow.
On the flip side, if you're a small business trying to grow your company, this hole "carve out the market operating a loss in hopes that you'll make it big" idea doesn't work in your favor most of the time, statistically speaking.
Modest investment for modest gains for modest success for long term growth is the smarter bet for the business owner (usually), but that's not as flashy, headline worthy, or profitable for the investors as the go-big or go-home approach.
So, it depends on what perspective you're taking as to whether this "conventional wisdom" really is good or bad.