Lack of liquid water
Within a few million years of the planet becoming tidally locked, all the moisture would be locked up in a permanent icecap on the dark side of the planet. The light side of the planet would be drier than the Atacama desert in Chile.
The lack of water vapor in the atmosphere would lead to the dark side being even colder as water vapor is a major greenhouse gas.
Not habitable - even the area around the terminator would be totally lacking in water.
