People are at their most naked and vulnerable when either peeing or pooing as their most intimate areas are fully exposed.. Somehow, this can be very appealing.
As a kid, I was given a mighty soapsuds enema. At the time I had no clue as to what was happening, but found out very soon after. While the enema was working the nurse that gad given it to me, a complete stranger, sat on the tub rim inches from me and watched, or more correctly listened to, the enema working. A torrent of whitish water was followed by those distinctive plops of poo. Normally, I could not possibly have passed anything since I'm very pee-shy, but of course the enema completely removed that option.
While in school, if I needed help to poo, I'd take a disposable enema (in those days a Travad) like this:
https://medicolsa.com.co/liquidos-baxter/615travad-enema-rectal-baxter-bolsa-x-133-ml.html
to a remote public bathroom and use it in a stall, hoping nobody came in before I'd finished pooing. On one occasion someone came in just as the dose started to work and I struggled hard to aoid going until he'd finished and had left. Those were a very long few minutes. BTW, the Travad was pretty much a Fleet enema in a different package with a short hose that made it easy to take while seated on the toilet.
to me, the fun part of watching such activities is the feelings of embarrassment, and being helpless to retain until the watcher leaves.
In some videos I've seen close-ups of a person's openings as stuff came out, but this is a bit too much for my taste.
For me, if you're going to play potty games, seeing (or being seen) is an integral part of the lay sessions. But each to their own.