[throwawaymaths]

Too big to fit on an FPGA that you can afford.

[klyrs]

There are actually cloud FPGA offerings nowadays! They're downright affordable compared to retail price for the monster chips they're sporting.

[Sirened]

You can also do stuff like slicing your design and putting it on multiple FPGAs. Industry has been doing this for ages because there's no way in hell they're going to fit a full SoC on a single FPGA no matter how much money they can throw at that problem.