What would cause all my dimmers to dim less?
Virtually all new dimmer switches are "smart" switches.  They contain tiny computer chips that control the dimming functions, and most smart switches have internal "parameters" that can be set with values to define things like minimum and maximum brightness, dimming speed, brightness step levels, etc.  These switches often allow the user to change the parameters by holding the switch buttons down and tapping or clicking following a certain pattern.  

For some reason I've found that certain people have a knack for messing up these switches - perhaps someone is holding down the dimmer button instead of clicking the paddle.  It's incomprehensible to me how they manage to stumble into the pattern to mess up the parameters.  And it's pretty much impossible to guess how to undo the damage without proper documentation.  You'll need to read the manual for your specific switches to understand the different parameters and settings, and how to restore them.  

You may find it easier to perform a "factory reset" on the switches, but be warned this could cause a home automation controller to forget the configuration for the switch.  Then you'll find your lighting problems have suddenly become computer problems, and that's even less fun.

If they are part of a home automation system like Z-Wave or Iris, the parameters can be easily set and reset by the installer using the system controller and a computer.

As you read through the manual, look to see there is a parameter like "disable changing parameters from the switch".  If so, I recommend setting it to avoid accidental repeats of this problem in the future.