I think a lot of people don't seem to be able to understand it because they are thinking about it on an individual level .
Yes, you can be, for example, a white person who absolutely loves big afros or locs etc and you want to have them because they're gorgeous (equally applies to clothing etc, hair is just an example)
And so when someone says that's cultural appropriation you get cross because you feel attacked and you think that's really mean when all you did was genuinely love something and you think that's just not fair. You feel accused of racism and so you come over all offended and start telling people how what they feel is not valid.
However, the problem is not that you as an individual like a certain hairstyle, or outfit. It is that you as a white person ( to stick with the original example) will likely be told how great the style is and how good it looks. If you're famous you'll be in magazines being praised for your bold fashion. You'll not be judged for it or told it looks messy or unprofessional. People won't make assumptions about you.
And before you dismiss it, black women are put under huge pressure to straighten, neaten, "westernise" (aka white woman) hair. Imagine growing up feeling you're ugly, surrounded by messages that re-enforce that every day, getting unacceptable comments, being told by your boss that your natural hair is unprofessional, and so on and so forth
Cultural appropriation is about cherry picking elements of a culture and reducing them to fashion and either not seeing or consciously choosing to ignore all the history, bigotry, bullying, stereotyping, bias and absolute shit that someone of that culture or heritage faces.
Furthermore, the reaction to ca being pointed out is to dismiss it. That in itself is part of the problem .
People of colour being told how to feel and how to see something and being told no, your view about your culture or heritage is wrong and I, a member of a more privileged culture or heritage will tell you how you should feel, what you are allowed to believe and what you must not think.
All uses of the word "you" are general you not person specific you.