Why is Level 2 charging more than 2x as fast as level 1?
 

Why does level 1 take so much longer? For example on the Ford Escape Plug-in level 1 (110v 20a) takes 11 hours to charge while level 2 (220v 40a) takes 3.3 hours.

So using 1/2 the power takes 3 times longer? I thought faster charging created more heat/waste?

Level 2 charging has 4x the power so the times you list make sense assuming there is slightly more heat created due to the higher power level. Higher voltage going into the car will have less resistive losses in the wiring. And depending on how effective the battery and charger cooling system is, you may lose more energy just keeping everything running for 11 hours instead of just 3.3 hours.

Level 1: 110V * 20A = 2200Watts
Level 2: 220V * 40A = 8800Watts

240v is more efficient too.
12 amps of 240v is nearly 3x as fast as 12 amps of 120v, because it's more efficient.

I don't see that being possible. According to some sources charging at 240V is only about 5 and a half percent more efficient. Of course, it will vary with each setup, from the wiring in your home and EVSE to the charger on the car. But getting "nearly 3x" the charging for only double the power does not make sense in the lightest.

Plus you have to factor in the charge tapering off as it gets closer to "full." I bet that at a 12 amp limit, charging at 240V actually takes longer than half of what it would at 120V even with the small increase in efficiency.

As far as the original question goes the OP was assuming that charging at twice the voltage and twice the amperage was only twice the power, where in reality it's four times the power, hence why it takes close to a third the amount of time. It's about a third and not a quarter of the time because of the charging slowing down as the battery becomes full.

Efficiency does factor in, but it is small in comparison to the four times the power of the level 2 charger.

You left out time. Both 120 and 240 have similar losses in the moment, but level 1 charging has those losses for at least twice as long.
For example, the leaf level 1 charger sends at 1.4kw to the car, but only about 1.2kw makes it to the battery. That's pretty significant.
Slow level 2 charging is 240v at 12 amps, it sends about 2.9kw to the car and about 2.7 to 2.8kw makes it to the battery. Because it's more efficient to step up 240v AC to 400Vdc as opposed to 120vac to 400vdc and now you are losing those roughly 200watts for less than half the time. Also level 1 charging is 1.2kw and level 2 is more like 2.8kw in this case.
Level 1 charging just sucks, for lots of reasons, just don't do it.

120V × 12A = 1,440W
1,240W ÷ 1,440W = 86%

240V × 12A = 2,880W
2,800W ÷ 2,880W = 97% 11% increase
2,700W ÷ 2,880W = 94% 8% increase

To me an 11% improvement sounds like an exaggeration, but still:

24kW ÷ 2,800W = 8.57h
24kW ÷ 1,240W = 19.35h
19.35h ÷ 8.57h = 225% increase of time, which is 75% short of ×3 improvement.

https://youtu.be/op9DbnVyp2M

A YouTube Video I just posted on building adapters to plug in my stock 120 volt EVSE that is capable of 240 volt operation into a 240 volt outlet. Do not try this unless your EVSE is truly 240 capable.

Most of this is due to unfortunate side effects of lawsuits and legislation specific to HK & USA

Certain EVs will charge up to 30 amps on 110vac but most override the EVSE signalling for high speed L1 giving you artificial 8 or 12 amp limits to limit to possiblity of fire damage to worn and cheap outlets

Outside the leaf with 30amp 110vac RV compatibility L2 has speeds up to 240x72amps sadly few onboard chargers ramp that high

Summary

Portable L1 (typical) 6-12 amps @ 110vac
660-1440 watts

Leaf 110vac EVSE up to 30 amps @ 110vac
3.3kw

L2 (USA) 10-72 amps (max) at 208-240VAC
2.08 - 17.28 kw

The US for lack of standardization does have lots of possibilities if the onboard charger supports

Always disappointed me that few EVs support 110vac at rates higher than 12 amps

Kinda glad to have proper electrical systems over here, we have 380V 3-phase in most houses, even if many do not have outlets for that yet.
So typical at home charging speed here is 11 kW for EVs, although our AC modes are:
L1: up to 3,7 kW single phase 230 V
L2: up to 7,4 kW single phase 230 V or up to 22 kW 3-phase 380V