>I want an honest answer.... I don't understand why many still cling to him...
The problems Marx addressed were popular problems, and have remained popular to this day. Keeping that in mind, it's easy to understand why one of the earliest and most prolific authors on the subject of capitalism and its connections to those problems is still widely read. Easy, that is, unless you've not bothered reading any of his work yourself and don't trust anyone who says it's worth the time. Marx had contemporaries who were better known, more prolific, and respectable to boot. Their work just wasn't that good, so no one gives a shit about them anymore.
>Is it nostalgia, many people simply can't leave the 60s alone.
I genuinely can't tell whether you're an out-of-touch antiquarian referring to the 1860s, or a philistine who thinks Marx wouldn't matter if people would get over the 1960s.
>is it more of an aesthetic appeal to the ideas of Marx, without actually thinking about its practicality
Marx rarely suggested practical models for anything, and the exceptions were very context-sensitive. You can't take the Critique of the Gotha program or the Manifesto and try to make it a modern political platform—that would, ironically, be fundamentally opposite Marx's method for forming those historical programs. If you spent any time actually engaging with Marx's work, you would know that.
>I think many academics remain marxist, not because they honestly think it is applicable, but because that is the reference frame they have viewed society through their whole academic career...its hard for many to adopt a new approach
His work was good. As is usually the case with good work, it was built upon and adapted. However, I suspect you mean 'Marxist' as a political slur rather than a type of analyst. There is no simple way to explain this to the uninitiated. Marxism as a method of work is not a political movement or ideology. I understand that it is popular to use the term as a reference to the Soviet Union or a specific brand of socialist ideology, but popular usage has no place in academia where terms must have definite meaning.
tl;dr: People 'cling' to Marx because his work was good.