Because you appear to misunderstand Clever.
Clever is simply replacing the existing processor of schools having to coerce CSVs and other horrible formats and them them off (over email sometimes) every time data changes.
Schools may or may not buys apps that help determine teacher performance. Clever may or may not be used for moving the data. However regardless teacher unions not be effected differently with Clever as opposed to without.
We get love from teachers all the time at Clever (which, as a former teacher, makes me incredibly delighted).
Schools are using more and more technology (see http://edsurge.com/ for some examples), but often the burden of tech falls to the teacher. I remember burning the midnight oil manually setting up class rosters in MasteryConnect as a teacher, and fighting "roster rot" as students switched in and out of my class over the course of the school year.
With Clever, teachers get to focus on using the tool with their students, instead of managing data. They love it!