Obviously, the SEP isn't perfect, but it's a great place to start. There's also the Internet Encyclopedia of Philosophy [1]; however, I find its articles to be more hit or miss.
I say this as someone who had the opposite experience: I had a decent humanities education, but an abysmal mathematics education, and now I am tackling abstract mathematics myself. It's hard. I need to read sections of works multiple times. I need to sit down and try to work out the material for myself on paper.
Any impression that one discipline is easier than another probably just stems from the fact that you had good guides for the one and had the luck to learn it when your brain was really plastic. You can learn the other stuff too, just go in with the understanding that there's no royal road to philosophy just as there's no royal road to mathematics.
But if you can't even narrow the breadth of possible choices down to a few paths that can be traveled, you can't be surprised when people take the one that they know that's also easier with more immediate payoffs.
When "struggling through" a philosophy book, that doesn't happen in my experience. In fact, if you look up what others thought that passage means, you'll find no agreement among a bunch of people who "specialize" in authors who themselves "specialized" in the author you're reading. So reading that stuff I feel I have to accept that I will never understand what's written there and the whole exercise is just about "thinking about it for the sake of thinking". This might be "good for me" but it's really hard to keep up the motivation. Much harder than a math book.
You can take an entire mathematical theory on faith and learn to perform rote calculations in accordance with the structure of that theory. This might be of some comfort, since, accepting this, you can perform a procedure and see whether or not you got the correct result (but even this is a generous assumption in some sense). When you actually try to understand a theory and go beyond that to foundations, things become less certain. At some point you will accept things, but, unless you have enough time to work out every proof and then prove to yourself that the very idea of a proof calculus is sound, you will be taking something on faith.
I think if people struggle with doing the same thing with literature/philosophy, it's probably just because of a discomfort with ambiguity. In those realms, there is no operational calculus you can turn to to verify that, at least if you accept certain things on faith, other things must work out...expect there is! Logic lords over both domains. I think we just do a horrible job at teaching people how to approach literature logically. Yes, the subtle art of interpretation is always at play, but that's true of mathematics too and it is true of every representational/semiotic effort undertaken by human beings.
As for use, social wit and the ability to see things in new lights (devise new explanatory hypotheses) are both immediate applications of philosophy and literature, just like mathematics has its immediate operational applications in physics et al.
It's almost offensive - are technologists so incapable of understanding philosophy that Yudk has to reduce it down to the least common denominator they are all familiar with - some fantasy world we read about as children?
Even better, I'd like some filtering out of the parts that are clearly wrong.
That's why you have people arguing over what someone meant. Dumbing it down or trying to write something unambiguous doesn't actually make it better.
Original philosophers have the right to define their own terms. If they can't define them clearly, then they probably aren't thinking clearly enough about their ideas to be able to talk to the rest of us about them. (Unless they consider it more important to sound impressive and hard to understand. But if that's the case, we can say "wow, you sound impressive" and then ignore them.)
The top scientists in AI can't explain how their models make certain decisions (at least not deterministically). Computer code is notoriously gibberish to outsiders. 90% of programmers probably couldn't explain what their job is to people outside of the field. If they can't explain it clearly, should they also be forbidden from speaking publicly until they can?
Is it possible that you lack the background to understand philosophy, and thus philosophers should rightly ignore your demands to dumb down their own field? Why should philosophers even appeal to people like you, when you seem so uninterested in even learning the basics of their field?
Nor do I regard the line as being "things I understand". I'm not (usually) that arrogant. But if, say, even other computer programmers can't tell for sure what you're saying, the problem is probably you.