Have FPGAs been evolving very slowly? Modern CPUs have some 20 billion transistors and these limitations don't seem to have grown at the same rate since the '90s the last time I looked at them.
FPGA's also have billions of transistors now, but adding more block memory means removing transistors from something else, such as LUT's, registers, DSP blocks etc.
As always it is a tradeoff, and given many designs don't need much block memory, or need so much memory that external memory is a better choice anyway.
