What causes airfare prices to be incredibly cheap at times?

For example: On atleast 3 different occasions, I have stumbled upon airfare from Milw, WI to Phx, Az For only $40 one way.

It is usually Frontier airlines. Which offers these deals. But last time it was American Airlines.

What causes flight prices to be this low? When can I get lucky and find something this cheap again?

Will airlines no longer hire 2 pilots due to single pilot airliner?

Because of that I can't get enough sleep I worry people like my friends age and my nephew's age kids will never be airline pilots

Just hope someone address pilot shortage in America because I rely on air travel because it is faster I reach my destination quickly

I just hope single pilot airliner never happen because I would not trust a robot and I do not trust a single pilot airliner I hope there will be enough pilots because I hope children like my nephews age 4 through 21 will b3 be pilots single pilot airliner not safe but 2 pilot airliner is safe

Because you can't rely on computers because they fail sometimes

That is why I feel safe with 2 pilots on board

Is Wizz Air strict with hand luggages sizes?

With Ryanair I always take my big backpack (60 L but not completely filled) in hand luggage. It is a bit bigger than hand luggage size requirements, but it always passes (the weight is less than 10kg). Would it also pass with Wizz Air, or are they much stricter?
Stories of experiences are welcome!