Why does everyone drive 10-15 miles above the speed limit?

Because speed limits are not strictly enforced

Why don’t we raise the speed limit if that’s how fast everyone wants to go?

Because if that happens that any per-textual stop the police want to do needs an another actual crime being committed before they can stop you.

Why is traffic enforcement given to very expensive and ineffective police instead of cheaper and more automated traffic cameras?

I reject the premise. Traffic enforcement isn't very ineffective because the majority of people aren't driving 50+ MPH over the speed limit. Also, its not that expensive because your premise suggests that if we had cameras, we'd need fewer police. I don't think that's the case. When an emergency response is needed we need X number of police to respond. Therefore X number need to be employed and on shift at all times. If we have the expense of traffic cameras, its not going to reduce headcount below X, and we now have the additional expense of purchase, install, and maintenance of all those traffic cameras. The cameras have an headcount overhead of staff of their own.

Traffic cameras also introduce mistakes of their own including misreading plates, or thieves using stolen/copied plates, which would otherwise ensnare innocent citizens.

It’s a serious confusion I have about how society is supposed to operate because it seems like a complete and total breakdown of logic and sense.

I think you're looking at the rules and assuming the logical outcome is the desired result. Change your mindset. The desired result is what happens when human society is given a set of rules and reacts to them. The reaction is the actual desired result. The set of rules is simply one step to get there. In short, humans aren't 100% logical nor are they 100% rule following, knowing that, you establish a set of rules that you know will have some violation and you account for that in rules.