They keep it simple to understand and use in a practical sense. Similarly, the way they explain lift generated by an airfoil is incorrect.

Most instructors understand hypoxia as lack of oxygen, but think about this. The atmosphere composition. 78% nitrogen, 21% oxygen, 1% other gases. The 21% oxygen NEVER decreases, it is mixed throughout all the atmosphere layers, so it’s illogical that the percentage decreases. However, air density thus its pressure do decrease as you climb, so it’s harder to get that oxygen into your bloodstream

Explains why pilots on ATC recordings who have had a rapid decompression have that loud breathing sound from inhale exhale process.

You're just built different.

No most passenger airlines can't fly above 38,000 Feet. Even at that altitude the pilots can rapidly descend to 10,000 feet. If you have all engines fail the masks will deploy to provide supplemental O2 but the aircraft will still maintain pressurization just slowly bleed over time. If you have a rapid decompression and engine failure you would probability be screwed.

If there is a rapid decompression (like a bird strike on the window of a pilot or first officer). They have the last version they put on and the O2 masks drop in the PAX dept. Pilots do Mayday call and ATC acknowledges and plane does rapid decent to 10000 ft. This all happens in quick succession. FA's immediately take the closest seat and buckle up because the plane is about to do a nose dive like you have never felt. Airlines commonly fly a cruise altitude of 33 to 43,000 feet. Particularly more recent plane models flying long-haul or transcontinental routes like the B787 or A340.