What can cause 3-way switches to go bad? 3 quit working in about 2 months
Were all three of those switches installed with poke in wire terminations?

If so then that is likely the root cause of the problem. Move the wires to the screw terminals on the new replacement switches. In the cases where there are more than one wire in the set of poke in holes for a given connection those poke in connections should be replaced with a twist on wire connector to join the wires and an added pigtail that then goes to the switch screw.

Another possibility is that the builder used the absolutely cheapest possible switches. With high usage such cheap switches do not last forever.