I'm an almost entirely frontend dev (iOS + macOS now, web development in the past) and this is what I've come to believe. It's easy to program UI cleanly if it's extremely basic or not very usable — but the second you want an animated transition between states, or to remember what the user checked on the last page so that you can keep it checked on this page, or any number of other things that you need to do if you actually want people to _enjoy using your software_, it gets much harder.
My take is it's because building UI is building software for humans, and humans often want behavior that doesn't allow for clean abstraction. Backend dev is more about building for other software -- not that it's easier, just a different set of problems.
Never really thought about it this way but I completely agree
In a way I find this meme even funnier now because of how backwards it is. Often times it's the backend that's really clean and organized and the frontend is a hot mess.
Everyone always likes to blame the front-end engineers for being slovenly, but my experience is that; UI is just messy. It's just hard to program cleanly.
Not to mention, modern UIs are generally more complex than the old VB days (at least, my programs are): they have to adjust to various screen sizes. They are almost always client/server apps and need to account for more failure modes. They are built on top of a mess of a document layer that was never intended to be an application layer.
This last point is the reason the front-end space has so much churn. It's still an unsolved problem, and may never be well-solved, but I'm glad folks are trying to solve it. React was a step-change for me in terms of building better UIs. I'm looking forward to the next step-change.
Lastly, before someone makes the argument: no; we aren't going to stop building applications on top of the DOM + CSS. Not until someone comes up with an alternative that gives us the same ease of distribution and broad base adoption.
Edit: I should note, I'm a full-stack dev, and have been more back-end than front-end for most of the early part of my career. The backend is always easier for me at least, but I don't think it's because front-end devs are hipsters.