Bad main breakers are surprisingly more common than you'd think especially when the panel was installed in the 70s and never touched. Odds are the main probably won't ever trip. I've had people not even know where the main panel was let alone the point you're supposed to test them regularly.

I seem some shady shit... lots of double taps (most I seen was quad tapped), I seen mains jumped out cause "it kept tripping"...

An entire house on 2 50A breakers. (This was the quad tapped)

Wires tied right to the bus without a breaker even present.

Load distribution in the house is totally dependent on how it's wired and the service available. There's still places where I live with 60A service panels being fed 200A. Almost no one does shit to code unless you're a service tech or trying to sell the place. Not to mention some of the code inspectors in the area are easily bribed.

Copper being stolen from utilities is like the most common thing in vacant houses here.

However usually the reason shit gets so bad is because the county code doesn't require ANY permits or inspections for work on the existing interior of the house, only exterior modifications like an addition and anything with a service upgrade. You can legit call the power company here tell them you need a meter pulled to replace the panel and they will come pull it, and when you call back they don't even ask if it was inspected half the time if you sound like you know what you're doing.