Hmm ..... on the face of it, agreed, showers WOULD be a requirement.
On the other hand .........
Showers are not the deciding factor for ALL pax - as illustrated by the fact that on a number of sectors I recently flew with Emirates in F (the most recent being just yesterday) I was one of a fairly limited number of folk, from what were on occasion near-full F class cabins, who made use of the shower facility.
Etihad may perhaps feel that a) there are better (more innovative ??) things to do with the space taken up by two shower 'suites' and b) they want to be seen as trend-setters rather than followers.