I think we Brits are culturally different from the Americans, which is (in part) why this is the way things are here. I'd say, as a general rule, most Brits don't want to be the next Donald Trump, Richard Branson, Steve Jobs, Bill Gates or whatever. They'd be happy to just carve out a nice living from a job they enjoy. As such, the 'killer instinct' that so many of the 'big' American business leaders demonstrate (or write books about) isn't something we have much of. As a result, if you haven't generated any income (ideally a modest profit) then you're probably not going to make it because you don't have any "killer instinct" at all. A modicum of income/profit shows you're at least able to operate that way, and so may have a business that's a good investment.
I am of course generalising a lot here, and there are plenty of exceptions in both directions that either prove or disprove what I'm saying. You get the idea...
As for Dragons Den... I'd love to have a product that's an absolute no-brainer. I dunno, maybe an anti-gravity drive, or a teleporter or something. Then I'd like to rock up to Dragons Den, and ask for a million pounds in return for 1% of my business, just to see what they'd do.
And just to stay on-topic: I've visited Silicon Valley a couple of times. It's sunny almost all of the time, and generally I've found the people to be pretty nice. It's way, way to spread out though, so you have to drive everywhere (which means no after-work drinking). Probably just as well though, as it's something of cultural vacuum in my experience. A few places are nice enough, but not a great deal of depth to anything as far as I can tell. I'm sure the locals know better places than I ever found, but San Francisco, by comparison, is a far more culturally interesting place to live (and you can get public transport home after going out).