NASA is putting pause on sending commands to its Mars exploration instruments from November 11 through November 25 as it waits out the Mars solar conjunction. With the sun in the way, any commands sent to Mars could suffer interference capable of harming the robotic explorers.
We use very large radio dishes to communicate with craft at Mars, so that the spacecraft can use smaller dishes and less power. In order to add a relay at L4/L5, that relay would also need very large dishes and high power usage to reach the craft at Mars. Probably larger than anything we have in earth orbit today.
Could we use lasers instead of radio, like the Starlink laser inter-links or the NASA ILLUMA-T/LCRD demonstration?
Maybe in the future, but the existing Mars orbiters need to hear a strong radio signal. And laser communication has not yet been tested outside of Earth orbit. It will need to be significantly scaled up to handle the 2-3AU distance.