Possibly because they are not teaching on airliners? I'm sure if they were teaching on airlines, they would teach airline techniques!
Personally, I was taught:
1. Red Beacon on prior to engine start (as long as you have them, of course - some of the aircraft I fly don't). Nav lights only at night.
2. Wing/tail white strobes on as the airplane taxi's on to runway - again, as long as you have them.
3. Landing lights, except at night, I wasn't taught to use as the norm. I watched my instructor use common sense to switch them on in a very busy circuit, and I try to use the same common sense myself - use them when they will help. For my CPL, I was taught to use the landing lights for every take-off and landing.
Also, there are plenty of aircraft out there whose generators/alternators can't supply enough power to keep all of those lights going all the time, so if you are spending time in the circuit, you'll end up with a flat battery if you have everything going. The airline way of doing things is not the only way of doing things, and to teach it as if it is the only way is, IM(V)HO, no better than to not teach it at all.
FFF
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