Even the tiniest studio apartment in the UK would come with one. You very rarely see laundromats in the UK (usually in areas with a very high concentration of students, as halls of residence provision can be poor for them).
Why don't they have them in the US? You have water and electricity, so I can't understand why this is a big deal.
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.
When the tenant does finally move out, it's not uncommon for the landlord to renovate, add modern amenities, and raise prices significantly. Hence in-unit washing machines are on the rise and laundromats are on the decline. But it takes a long time for the process to play out.
Condenser dryers are pretty easy to install - all you need is an electrical outlet.
However, it looks like they're about 3x the cost of a vented dryer.
And smaller capacity than vented ones.
> Ventless dryers also take longer to get your clothes dry. A vented dryer might finish a Normal load in about 45-50 minutes, but a condenser or heat pump dryer could run for an hour and a half. Want to dry a bulky blanket or comforter? You could be waiting more than three hours.
http://laundry.reviewed.com/features/everything-you-need-to-...
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.
It's also possible that there's an expectation that you always have a washer/dryer combo, whereas having just the washing unit isn't uncommon from what I've seen in the EU/other parts of the world and then just having an air drying rack for drying. I was a little surprised when I first moved abroad at not having a dryer (and annoyed admittedly), but I got used to it pretty easily and just adjusted my laundry schedule. Likewise, the size may be a difference in expectation, as many people expect full sized units installed, not compact units.
Plus a unit with an in-unit washer and dryer generally costs more than a similarly sized unit, and part of that space is taken up by a washer/dryer.
(Aside: as it turns out, I didn't know how washing machines worked, and I spent like a year washing my clothes without soap before the attendant told me. I now know that a "pre-wash" is... exactly what it sounds like, and it's not compatible with putting detergent tablets directly in the drum.)
Also, a lot of landlords will rent out washer/dryer sets to tenants for another monthly fee if they don't have their own to hook up.
