There could be several reasons to issue single-use escape hood rather then full-face masks/respirator with changeable filters:

Facial hair: If any of the employees have beards or other facial hair that could interfere with the full-face mask/respirator from sealing correctly, they cannot be utilized. It might make it a challenge for the employer to set a no facial hair policy.

Fit and respiratory compliance testing are required annually for the use of a full-face mask/respirator. Each employee would have to receive a respiratory evaluation to make sure they can use a full-face mask/respirator and must then also be fitted with a properly sized full-face mask/respirator.

This could end up costing the employer more then simply issuing a single-use escape hood.

Pete