The biggest mystery in the whole thing is why someone who is volunteering to review papers anonymously would bother to do it badly when they could simply not do it at all.
* You do get academic points for chairing a conference, and as a chair, you do need to find reviewers.
* A colleague is running a conference, and asks you to do a favor. You want to help your colleague. Reviewing papers wins you points with them, and declining to review burns bridges. When you're running a conference, you'd like them to reciprocate. Plus, they might be on a grant / hiring / etc. board / committee / etc. later on. Burning bridges in academia is very bad.
On the other hand, there is no incentive to invest more than 30-600 seconds per review. Neither you nor your friend really have any reason to care about the quality of the conference.
As this process repeats, people put in less and less time each time around, since it doesn't matter. The process converges to random noise.
Why would they care? They get their name as the chair of the conference on their CV. No one remembers who chaired a specific year or how a given year went. If they did, there's enough noise in the process it wouldn't be attributed to the review process in particular. Some years, weaker papers come in, and others, stronger ones do.
Just accept people who has held a lot of conference talks before and it will be fine. That is the fastest and easiest way to review, so unless there is pressure to do things differently that is how most will do it.
If there is space still left at the end you can look at the others and take the first paper that looks fine until there are no spots left.
There is (for good reason) more focus today on diversity--broadly defined e.g. new speakers--for non-academic conferences these days. However, there were quite a few conferences in the tech sector historically that tended to have a core of "the usual suspects" with others grabbing a smaller number of leftover slots. TBH, I probably benefited from this over the years. (Conferences run by companies follow somewhat different rules but still usually have a stable of Top Rated Speakers who tend to get slots.)
