Why do engineers learn all this unnecessary math? Ex: Infinite Series, Limits in 3d, etc

It's all done by computers?

If you consider an engineer to be one who actually understands the material, rather than just running programs, the answer should be obvious.
Someone that just runs programs is NOT an engineer; they are usually called a technician or a designer. And needs a real engineer looking over their work to watch out for those times the program gets it wrong.

As a chemical engineer I had to take a LOT of math. There was absolutely no way I could have understood ChE Thermodynamics without multivariable calculus and PDEs, and likewise for Transport of Mass, Momentum, and Energy.

Trust me, infinite series are trivial compared with what you need to know.

There is no unnecessary math on an engineering course. Depending what field you go, you will use more some parts of math than others, but the understanding of how the world works needs physics and math. If you do not understand how are things, you will never be (a good) engineer.

For one, it helps to know what the computers are actually doing so you can tell when it's doing something wrong. But also, who do you think writes the computer programs?

You think math isn't important for engineers??? You aren't going to get far in this field. Computer don't do everything. An engineer who lacks an understanding in mathematics is useless.

Nova is a little blunt, but I agree with him.