As was already stated, they'd been theorized for a long time, the first one discovered was very much specifically looked for, not stumbled upon.
As far as destroying everything it ingests, and why it's not a funnel, that's all to do with gravity.
Gravity is by far the weakest force, but in a black hole, it simply wins.
The density of matter is so great, all the other forces are for lack of a better term, over powered. The forces that hold atoms together to form molecules, the forces that hold particles together to form atoms, particles that make up light, all fail to the might of gravity, all get pulled into what is called a singularity.
What is a singularity? Well, no one knows. It's what is at the heart of a black hole, it's whatever is left when everything is smashed into a point that not even light can escape. There is very complex math describing singularities, which I don't pretend to understand, but in all practical sense, we don't know what it's like in there because we have no way of reproducing those conditions or look inside one.
The point of no return in this gravity well is called the event horizon, and it's just about the only meaningful way to judge the size of a black hole. That and its mass.
It is theorized that energy/mass can radiate from a black hole, when spontaneous particle pairs form along the events horizon in a energy into matter solution to E=MC2, where one has enough momentum to escape, and it's pair does not. Under lab conditions these virtual and opposite particle pairs usually just destroy each other and return to being energy.
Not sure where the debate is at now, but the information loss caused by the destruction of this matter over here, and the formation of new unrelated matter over there, was a big deal in physics.
A back hole was the answer to the question, what happens when stuff gets so packed together gravity just wins? Discovering one in nature proves that that can actually happen.
It's also the spot where much of known physics and math just breaks down. We study them, but they really are a true mystery to science.
As to why it's not a funnel, well, in theory it sort of can be.
If the black hole is large enough, the tidal gravity forces increase gradually enough that a person could survive crossing the event horizon, though it would be a one way trip.
The time dilation caused by the high gravity means that time would slow down, functionally stop, from point of view of an outside observer watching this jump.
From the point of view of the spacewalker looking outward, time would speed up, and in principle they could watch the entire rest of the history of the universe play out.
Unfortunately, from their point of view in relation to falling into a black hole, time would just go on ticking, until the tidal forces grew strong enough to turn them into spaghetti.
It's what I've heard it called. The closer to the center of mass, and the smaller the black hole, the greater the change in gravity as you get closer.
The pull at your feet and the pull at your head when standing on Earth is so close to identical that it makes no difference.
Picture it like the lines on a topographical map of an open plain, they're all spread out, almost no change over a long distance.
The more you fall, the closer the lines get together, so that the gravity up top isn't the same as at your feet anymore, and that difference only continues to grow.
When the change in the gravity rate is high enough, the pull on your feet is so much stronger than at your head you get pulled apart like taffy.