All small MFH's (Duplexes, Triplexes, etc) very old?

[Cameron Iarrobino]

Hi BP community, I was curious if anyone local or anyone in general might know more about something I've been wondering about lately. When I look at small MFH's for sale on the market, and I've been looking for over a year now so have seen several dozen, it seems that almost all of these types of properties are late 1800's / early 1900's build. For context, I live in the Boston suburbs and am always looking in this area (Norfolk county specifically for any local people, own 1 duplex in Franklin).

It seems that all new-ish constructions are either SFH's, condos, large apartment buildings, etc? Does no one build duplexes, triplexes, etc anymore? Is this a known thing or is it just an anomaly? I guess from a developers perspective, I'd take an educated guess that if you had 2 properties right next to each other, identical in size, lot size, bedrooms bathrooms etc, but 1 a MFH & the other a SFH, it seems that the SFH would sell for more, and probably cost less (less framing, doors, windows, appliances, boilers / furnaces / water tank etc