Nice new house. Of course it has two sinks in the master bathroom. Why not? The cost of a second sink is a rounding error compared to the total cost of construction. The lack of bitching over the state of “my” sink is priceless.
We also have 2 dishwashers. These are awesome and used daily (we have 3 kids) instead of as I thought only at holiday’s or with parties. We never have dirty dishes piling up in the sink.
That and no children. 
I think the answer to the OP is that it’s not uncommon and has become increasingly more common.
My parents house is 1966 I think. There is just a half bath in the master bedroom. The full bath in the hallway doesn’t have room for 2 people. My house from 1969 doesn’t have a master bathroom (“en suite”) and the full bath has no room for another sink.
Watching home fixing & buying shows, it would seem that double master sinks are an absolute must these days.
My friend just reno’d their kids’ bathroom and put in a second sink. Their master still has one sink. So far.
I always thought that setup was one sink and one urinal…
House from 1978, master bath has 2 sinks. Last 2 houses have had this as well. I like it because I can keep things around my sink the way I like, and he can do the same.
I would like to change the kids bath to have two sinks as well. 2 kids and the arguments they get into over the sink makes me crazy.
Nope, house was built in 1967, the ensuite bathroom is tiny. One sink, shower stall only. I use the bathroom down the hall and gave the ensuite to my husband.
My ideal house would have a master bedroom with two separate ensuite bathrooms. Two sinks in one big bathroom just means we would have to suffer each other’s messes. My husband is neat most places but a total slob in the ensuite bathroom (because no one else will ever see it).
We also have two sinks for the commoners.
Yeah, what’s up with that? Our condo is rented most of the time, but when we stay there, my husband and I only use one sink. Given the opportunity, you’d think we’d spread out a bit more, but I guess we both like spitting our toothpaste dregs into the same receptacle the SO uses. Must be twoo wuv.
I first noticed this when on a home exchange to Amsterdam. They were a professional couple, so presumably both needing to be out to work fairly sharpish in the mornings, I think.
In a one-bathroom apartment, for that sort of owner/resident, it makes sense to me - a couple doesn’t necessarily need to be in the bathroom at the same time to value having their own individual spaces (I’m thinking as much over-basin cabinets as the basins themselves). I’ve got just enough space to do it in my bathroom, which will soon need a makeover, and I reckon it will add value.
Previous house (built in 1992): two.
Current house (built in 17th century, bathroom from 1990s): one*
*really not enough space for 2, and bath, and shower, and toilet.
My house has one bathroom and therefore one sink.
The house we just bought this year was built in 1979, and the kitchen/bathrooms were updated in the last 2 years - our master bath has 2 sinks. Photos of the ‘before updating’ show only one sink, so maybe it’s a modern thing now?
The other bath has one.
None in the kitchen?
I don’t think it’s necessarily a recent thing. The house I grew up in had two sinks in the bathroom. Built in 1968.
My wife and I have been house-hunting recently. Double sinks aren’t absolutely ubiquitous, but they are very, very common, in houses of all ages. Sorry, I’ve got to say that your mom is more right than you are.
My house has two sinks. In fact they are “his and hers” style with the “his” being about 2 1/2" higher than “hers”. My lake house also has two sinks, but both on the same plane. The guest baths in both houses have one sink. Two sinks are the way to go if you have the room.
The MB in our house has two bathrooms, completely separate! There is a bathroom and closet combination on two different walls. One dead ends, and one is a pass-through (there is a third bath in another part of the house for guests).
Each has only one sink, though.
I don’t know what they were thinking with the design. It’s wasteful of space. We never use the one for its intended purpose (it’s now a storage room).
Does the pass through bath connect two bedrooms? We usually call that setup a jack and Jill bath.
Two sinks in a mb is so common here in Chicago suburban houses as to be notable by its absence. In the city with older housing it’s less common but high on most lists of wanted improvements.
Mike, kitchen and bath designer for a few decades now.
My house was built in 1968 and doesn’t have a master suite. Sorry.
I’ve lived in several houses in my time and when house hunting I have never seen a bathroom with two sinks. So you are right and your mom is wrong.
Just bought a house built in 1993. The master bath has 2 regular sinks. The laundry room/half bath on the lower level also has 2 sinks, one bathroom sink and a utility sink. The other full bath in the house has a vanity with enough room for 2 sinks but has only one.