Number of strides can be adjusted easily at 400m. Not so in the sprint hurdles. The 100 and 110 variance is necessary to allow both genders to 3 step.
Partially true. They can keep hurdle spacing the same for the women's hurdles and still run 110 meters. They would just have a longer sprint to the finish after the last hurdle. The women currently participate in a 110m hurdle race for the shuttle relay which is a relatively new phenomenon started in 2019.