Overarching Idea: In every university I attended and worked at in America, the idea that was shared by faculty and students was that students were there to learn from professors who are subject matter experts, whether those classes are general education classes or classes in their major. And that graduating from that university reflected not just having majored in a single field but being well rounded and having achieved a standard of learning to make one worthy of the degree.
Corollary 1: for most fields, if someone can cheat on your exam easily, then you're doing something wrong in terms of teaching university-level material.
Corollary 2: a university should not be a war between students trying to cheat and faculty trying to catch them.
Consequence 1: Try to attract students who actually want to learn to the maximal degree of selectivity your university can handle.
Consequence 2: When cheating might have happened, once it's been confirmed it did, then severe consequences follow.
In nearly all the universities I worked in, the consequences for plagiarism and other forms of cheating were severe. I think the most lenient was a two-strikes policy (as in get caught cheating twice and get kicked out of the university with one or two academic misconduct marks on your transcript).
Based on this idea of the university, it doesn't make much sense to do a lot of video surveillance to ferret out cheaters. (Who would watch it? Who pays for installing it?) Moreover, the stakes of a very small percentage of people effectively cheating are high for the individuals but low for the instructors and the university's reputation.
In the case of ETS, there are other reasons why it makes some sense for them to do so. First off, they are in the business of assessing particular individuals' abilities both with the GRE and TOEFL, and they have little contact with the people outside of the tests. If cheating scandals occur, the stakes are high for both the individuals and ETS, because the security of their tests is a big piece of their business.
To put that another way, University X's reputation as a good place to go is largely a function of the sort of faculty it has and the research and teaching they do. Minutely, it also includes that you can't buy your way to a degree there. Conversely, ETS's reputation is all staked on them being able to help universities figure out whether students can succeed on the tests they offer (regardless of the validity of those tests).