It's not about taxes though. That's what so many people don't understand.
If you had a global behemoth of a company, and you were already based on the West Coast, then your links to Asia would be just about as good as they could be without relocating out of the US.
But what if you wanted to go for a whole "sun never sets on the British Empire" thing? Then you would need better links from the Europe-Africa side of the world to your HQ. Assuming you don't want to relocate out of the US, that means the Eastern seaboard. That's just geography. Which place on the eastern seaboard has the best multi-modal transport links to the rest of the US and Europe-Africa? NYC. For logistics, by air, land, and sea, you can't beat NYC. They've just invested way too much into that stuff for anyone else to beat them at it. (Probably did so over time using those high taxes you talked about.)
Add in the fact that NYC has access to an enormous community of technology experts, and the fact that it has plentiful high powered jobs in other industries, and the choice really is a no-brainer.
Dallas, is just not there yet, to be perfectly frank. The only city in Texas that is even working towards being a rival to NYC is Houston. And while they've made admirable progress, with ports, metro trains, and airports, they've still got quite a ways to go. (For instance, they're metro is building out nicely, but it still doesn't connect to either of their airports yet. Nor does it connect to their port.)
Other cities can compete with the coastal elites, but we have to sober up as to what we need to do in order to actually be competitive. Lowering taxes might be part of it, but it's not going to make any of the knowledge behemoths leave the coastal elite cities.
Would you leave your home for another home in a neighborhood with worse schools and worse transport just because it was cheaper?