You seem to think that any company can build any product.
In reality, you need some expertise to build a product.
A router is just not a piece of hardware. It's not just an Intel CPU, some RAM and 2 ethernet cards.
Anybody can make hardware.
As long as we're not talking bleeding-edge CPUs or GPUs, it seems there are a lot of chip-designers in the world who can make ASICs. The trick is to know what your ASIC is supposed to do.
But then, if you go build a router with a x64 CPU, you'll find that:
1) it gets too expensive
2) it gets too hot. you'll need cooling. never good for a device that's supposed to sit out of sight, maybe inside a cupboard of some kind. doesn't get proper ventilation.
3) cpu-speed is less important, what's probably more important is I/O of your bus, can you copy bytes (packet minus headers) straight from ethernet-card to ethernet-card. And do your feature allow to do this, or do you have features that require you to copy/buffer packets into RAM first ?
And what are you gonna do with a high-end router ?
If low-end routers can do 200 Mbps bidirectional, you probably have covered 90% of the current residential market. If your low-end router can do 1 Gbps, you have probably covered 99.5% of the residential market. Even if you make the best high-end router in the world, you're gonna have a limited market to sell your product.
I think it's unlikely you can make a profit here.
And then there's the software.
Do you have people who understand all the ins and outs of various DSL and cable flavors ? Who understand all the finesses of NAT ? And then there's the rest of it all. You can go fetch some open-source networking software. But if you do that, what do you have to differentiate your product from any other product ?
There are lots of companies that will not enter a market, new or old, if they don't think they can be #1 or #2 in the market. If you start in the residential-router market now, it's unlikely you beat the existing players. If EVGA is like other companies, they won't even start thinking about starting.