I should have specified "traditional dryer." New tech is pretty interesting, I didn't know they existed, but then again I don't pay much attention to dryers other than my own and my own needs ventilation to the outside and a special plug. Price would certainly be an issue in a lower cost rental unit.
Also RE: "much less appealing," should have specified "much less appealing to a prospective tenant than a washer/dryer combo thus wouldn't command higher rent thus isn't worth a landlord's time and money even if space is available right next to the sink for a cheap install." Line drying is much more common in other parts of the world.
Plenty of apartments in the US have washing machines, I've lived in several apartments and all had a washing machine[1].
As for the reason why many don't - historical (they weren't designed when household washing machines didn't exist and were never retrofitted), and slumlords not wanting to manage another appliance.
Add to that nowadays Americans don't do much air drying of their clothes so a washer without a dryer is much less appealing. As long as you had physical space adding a washer to an apartment that wasn't designed for one is cheap. Adding a dryer is very costly - dedicated plug or gas line plus ventilation to the outside. So if it's not economically worth the dryer upgrade than most landlords just won't bother with a washer upgrade either.
If your landlord doesn't provide a washer and your apartment doesn't have washer hookups you could always get a portable washing machine (or jury rig a regular washer to be 'portable') for any apartment as long as you had somewhere to store it. I've even hear of someone splitting the water line under the sink to install a washer in a rental.
Same thing with dishwashers, some apartments have them, some don't.
[1]One apartment I lived in though had all the washing machines and dryers in the shared basement and they were coin operated and we weren't supposed to use them after 9.
Also RE: "much less appealing," should have specified "much less appealing to a prospective tenant than a washer/dryer combo thus wouldn't command higher rent thus isn't worth a landlord's time and money even if space is available right next to the sink for a cheap install." Line drying is much more common in other parts of the world.