Look at the exhaust, which is where the heat comes from. Nearly all MANPADS are infrared guided. The A-10 hides the engine exhaust by surrounding it with the aircraft's tail. An F-35 doesn't even try to be stealth at the rear, with a great big round hot orifice.
The A-10 can frequently survive MANPADS. It has two engines, physically separated on pods. The F-35 will crash if that single engine gets hit.
Tow a decoy if you want more protection.