Why MMICs (monolithic microwave integrated circuits) are built as drop-in gain blocks for standard RF systems, so their internal matching networks are designed around the universal RF test and system impedance of 50 ohms. That lets you solder one into a 50 ohm microstrip line with just a bias resistor and choke, no matching network needed. Nearly all RF test gear, connectors and coax used in amateur and commercial microwave work is 50 ohms as well.