TLDR: Often not, due to costs or incentives.
Lint is not a significant pollutant.
The major reasons are:
- The high construction cost of building a dryer vent in every apartment.
- The enormous energy wastage of taking interior air, which is already fully conditioned for temperature and humidity, and ejecting it outside. This is exactly the same problem as "1-hose" portable air conditioners... like them, a 2-hose dryer could cure it, but who's ever seen one of those?
- The air being ejected by the dryer has to be made up somehow - exterior air must now be let into the building. Even modern American construction is tight enough that you have to actively think about that - ordinary window and door seal leaks won't provide that much leakage anymore. Having to deliberately add leakage to support That 70's Dryer is not good for efficiency.
The upshot is, the traditional American "vented dryer" is highly incompatible with a number of best practices in HVAC design and efficient buildings. They are popular because they are cheap to buy -- that is a perverse incentive for Americans to keep buying them even though they are a net financial lose!
My next paragraph would turn political, re: how governments help (or refuse to help) eliminate perverse incentives, so I'll go ahead and not say it.
How it works there (and you can get them here)
Generally these dryers boil down into two technologies.
First is called the "Condensing Dryer". This takes the hot, wet dryer air and runs it through a heat exchanger with normal room air. This cools the hot air (at the cost of heating the room) causing some of the water to condense. The air is then heated again and sent back through the dryer. Wet air is NOT intentionally dumped into the room (that would be bad).
But honestly, this is not great. Ambient room air (think 65-100°F/20-38°C, not all European homes have air conditioning) isn't all that great for cooling the heat exchanger. And obviously the heat exchanger needs to fit inside a dryer! So they are slow as daylights. So they tumble for a long time, which is bad for clothing life.
The cure for those limitations is a "Heat Pump Dryer", which is basically a common freon-based dehumidifier inside the body of a dryer. It is doing the same thing, but using a Freon engine to do the "physics cheat code" :) It efficiently makes a 2°C/35°F "cold zone" for highly efficient condensing, and a proportional "warm zone" to preheat the air being blasted through the tumbler.
These work slick as a whistle. They simply need electricity (and not that much of it thanks to those cheat codes), and a drain to dump the water (they can coat-tail the washing machine's drain in most installations). They do not need gas, and in some cases do not need 240V.
I suspect the lint filter is also significantly hindering the drying efficiency but who knows ...
Not at all. First you don't actually mean "efficiency", what you mean is "drying speed" - not the same thing at all.
The poor performance is owing to "condensing" (non-heat-pump) dryers relying on ambient room temperature to get useful condensing. That can be very adverse if the laundry room is closed in and allowed to heat up. Heat pumps solve this by using those "physics cheat codes" to mechanically make a large temperature difference. They're still not quite as fast as a vented dryer, because drying is super easy with an unlimited supply of pre-conditioned air that was paid for by an "externality".
The self-economic pressure by cheap builders
These types of dryer tend to show up in the USA with large development builders (e.g. a big condo complex) where the cheap builder seeks to reduce the cost of installing the many utilities needed in a laundry room:
- Cold water
- Hot water
- Dryer vent
- 120V (for washer)
- 240V (for dryer)
- Gas (for dryer)
The cheap builder can whittle down utilities thusly: First, support only gas OR 240V (probably going to happen regardless). Use a washing machine with onboard water heater, that crosses off "hot water". Use certain models of washer-dryer where the washer daisy chains AC power off the dryer; 120V gone*. And as discussed, dump the dryer vent. The cheap builder has eliminated 4 utilities and are now down to 3: cold water, drain and 240V.
* eliminating 120V only works if it's a laundry alcove just big enough for the machines. If it looks like a laundry room a 120V/20A circuit is required per NEC.
The cheap builder says "I will pay more for the specialty appliances, but I save considerably more than that."
The government pressure
Governments like to promote efficiency, such as LEED buildings. As discussed, a "dryer vent pipe" is a gut-punch to HVAC efficiency. So when a builder is being incentivized, or mandated, to hit efficiency targets, eliminating the dryer vent is a "low hanging fruit". And yes, they are sometimes omitted in the most modern buildings.