Because users do not know that there's some hypothetical "better" experience they could have had and do not care, unless your service/tool/whatever is not functioning correctly. Prioritizing your employees' enjoyment and experience to deliver more, faster, and consistently, is in all likelihood a better decision than prioritizing some subjective improvement to user experience.

Of course there are exceptions. But it's definitely a hot take to say you should never prioritize DX over UX.