Huge on-die capacitor
The limit is just what you're prepared to pay. In a 0.13 \$\mu\$ process it would be a shame to waste all this space on a cap; you could place probably 10 000 transistors there.
The LM113 is already old and has a far larger feature size, so it will take relatively much less space, compared to the complete die. Don't forget all the resistors. Those are also expensive in die real-estate terms.  

Assuming a separation of 0.1 \$\mu\$ and a dielectric constant of 10 a 75 pF capacitor will be around 0.3 mm x 0.3 mm. Not that bad after all.