What's to "discover in a pool"? Maybe the instructor wants to find out if you can swim? If you're the type who has anxiety attacks or something else that might endanger him or her or anyone else?
As I recall Dive Friends Bonaire have a roped-off piece of sandy beach in front of the Yellow Sub. You don't drown and/or have a fit there, you can swim 10 more metres out and see the pretty fishes and corals.
The way I see it, a DSD isn't about seeing coral or fish....it isn't a Discover the Ocean experience. It is a Discover Scuba which to me means that you get a chance to feel what it is like to don a scuba kit and take that first breath underwater followed by a short swim.
The way I see it, there's people who are comfortable underwater and there's very little chance they'll have a problem breathing from an aluminum can. "Meh" is about all there's to discover there. And then there's people who aren't, and all that hassle with the gear just to sit on the bottom of a pool will likely provide them with something between zero and "meh" motivation to get comfortable.
If the purpose of the DSD is to create customers for the shops and agencies, then DSDs in a pool get a big fat F.