I think one reason why abstract concepts are still used is that it feels more artistic when all this indistinct eloquence is being tossed around. It implies deep meaning that simple words just can't convey.
I also think the other reason is that it gives the writer an excuse to be lazy. He doesn't have to explain anything in particular; he lets the reader attach whatever meaning he wishes to the words. I will suggest that sometimes it works well; sometimes I want to be given interesting, nebulous ideas and allow my own specific emotions and background to find meaning in them. I think that also is what puts that kind of poetry at a distance, since it forces the reader to do exactly that. It becomes an investment of effort that some folks just don't want to partake in.
As a result, unpacking things into clear words shows the reader exactly what's going on. It may be less subject to interpretation, but probably more accessible to a broader audience.
For sure, there is a belief found in many novice writers that poetry should be abstract, a struggle to understand and maybe even somewhat confusing. I believe people have this idea because this is how they felt when they were given older poetry to read, outside of the modern vernacular, when they were at school. Of course that was going to be confusing. Anyone faced by older poetry who's not accustomed to reading it is going to find it challenging at first. But that's not because it's poetry – that's because of the antique language.
I also agree, there is a place for abstractions in poetry, especially when it's warranted by the core idea, logical process or theme. That's when it really can add.
For the reader though, you're right, it's presenting them with more of a struggle.
And your last line says it all. You can write poetry any way you want, to be honest. This session and all the others I'm presenting are about what to do if you want to make your work reader focussed.
As always, Neg, thanks for reading and following along.