Maybe they’re trying to get on the level of a less observant Jews and nonJews.
Saying “We do this because it’s a commandment from G-d” may alienate unobservant Jews and nonJews.
For the record, when I was less observant, a rabbi told me point blank, “We do this because it’s a commandment from G-d” (in his words), and I loved it! It was refreshing to hear oneself speak in this way, instead of the sales-pitch approach –which I less prefer and can be a turn off.
So yes, I agree that saying that we do this because Hashem said so does require emuna and bitachon. At the same time, maybe observant Jews have more success saying it in other ways, or want to avoid confrontation. Avoiding confrontation in itself may supersede here, since it’s looking out for one’s pikuach nefesh.
Sometimes maybe it’s better to let the kiruv speciailists and rabbonim do the teaching.