There's both a cost and a speed barrier to it. FPGAs are often used to design, simulate, and test modern circuits at sub-realtime speeds. No amount of FPGAs will get you a PS2 emulator at playable speeds right now, let alone a PS3/Switch emulator. PCs can do that today by taking shortcuts such as dynamic recompilation and idle loop skipping.
Hmm... looking at the frequencies and gate counts, I think PS2 is well within realm of possibility to run on a not-so-cheap FPGA (or several). But PS3 generation consoles definitely not.
