Almost certainly it is something a prior homeowner had custom done. You won’t get a good answer online because this is the unique brainchild of whoever built it.
What makes you sure it was put in when the house was built, by the way? Could it have been added in later?
ETA: I see that you allow for a remodel in your OP. Others were saying it’s too small for a 60s style hairdryer, sure, but maybe the homeowner put it in in the 80s.
Looks like to me, but I did not inspect terribly closely. On the wall to the right of the photo, there is a recessed TP niche/alcove for the TP holder - deep enough for a spare roll behind. Lined with the same grey material. But - IIRC, lacking the wood trim.
The outlet is odd, seeing as there is another outlet right below it.
Sure, it is likely someone’s brainchild. But few of us are so terribly unique that no one else can imagine what they possibly were thinking. Rechargeable dildo perhaps? But, I see kayaker already mentioned the possible religious aspect…
Without seeing what the OP is talking about, I find bathrooms often have odd niches in places - perhaps because bathrooms are often quite small, so space being limited, a niche serves in place of a cupboard or shelf. My last bathroom had a niche in the shower. Presumably the electrical outlet would have been for a shaver, which seems to be just about the only outlet I ever see in a bathroom (I appreciate we in the UK have strict rules about these things).
Personally, I’d use the niche (or alcove) for a Thai Spirit House display. Since there’s an electrical outlet, I’d incorporate a nightlight bulb in the house.
My sister reminded me that my wife had given the niece some kinda light up doodad which had been in the niche for a while, but no longer was. Sis says there is a closet on the other side of the wall, which she has never looked inside.
I kinda get hung up over the fact that this bathroom is on the lower level of a trilevel. The middle level has the entry, living/dining rooms, and kitchen. Upper level has bed/bathrooms. Lower level has one bedroom, utility room, and large TV/rec room. Rec room portion has a large bar and had a pool table - currently has a gaming table. So this bathroom is the one that is most likely to be used by guests - if they are over to game.
We also have a split level, and our preference is that guests use the lower level powder room instead of going upstairs into our more private living space. If we were to have a hot foam dispenser/hair dryer/dildo/whatever, it would more likely be on the upper level near our bedrooms.
Missed the post, sorry! I’ve seen it now, certainly distinctive. People have all kinds of mad ideas about home decor. Can’t imagine why anyone would want a religious statue in a bathroom though! Even my ultra Catholic MIL didn’t do that.
She has a closet in her house that she has never looked inside of? I can’t imagine not looking inside everything when I first buy a house, at the least.
I suspect it was an artefact of a remodel. The original wall had the electrical outlet, and for some reason, they wanted to keep it, and built this nook to accommodate that.
I’ve stayed at hotels with phones in the bathroom, and they were all wall mounted. I’m not sure the typical landline phone would fit in there.
I’m going for some kind of statue, religious or otherwise, though why the outlet beats me.
If the niche weren’t framed so nicely I’d suggest hanging some art over it, but that won’t work as it stands.