Silicon Valley's great strength is the huge, fluid ecosystem of skilled engineers, executives, funders, and supporting professionals (lawyers, landlords, marketing consultants), all of whom are actively searching for "the next big thing" and want to be part of it. That lets you rapidly
scale a company when you've proven it out on a small group.
I grew up in the Boston area, and honestly, I thought there was more genuine technology innovation coming out of Boston-area institutions like MIT, other area universities, Lincoln Labs, MITRE, Raytheon, BBN, etc. The problem was that most of these innovations get strangled in their cradle, because Boston VCs are looking for ways to do things that are already being done better, and aren't willing to take a chance on ideas that look nothing like existing businesses. In Silicon Valley, you can usually find at least one defector who thinks "Well, it's a terrible idea, but I'm going to invest anyway just to see what happens." And that's why you have all these companies that actually started in Boston - Microsoft, Facebook, Reddit, DropBox, YCombinator - but are now known as either "Silicon Valley" or "Seattle" companies.