I’ll answer the question literally first, then offer some context.
Answer to question
There are multiple reasons why KDE’s developers don’t focus on just bug-fixing for two years:
You don’t say no to getting paid: A great deal of development in KDE is in fact sponsored by someone, and they often sponsor features. Saying no would mean less sponsored development in general, rather than a substitution of bugfixes for features.
It’s not realistic: The line between a bug fix and a feature can be blurry. Is implementing a useful Wayland protocol a feature or a bug fix? How about porting software to use newer libraries, backends, or drivers? What about improving the UI for something that’s currently awkward? These kinds of work are important long-term and cannot be neglected.
You wouldn’t actually want it: Even if focusing only on bug-fixing for two years were possible, it would make us fall behind the competition. KDE does not exist in a vacuum, and our software is always being compared to other options. Here is the full list of what KDE software wouldn’t have if we hadn’t implemented any new features over the past two years, just going by the naive definition of “feature” as "tracked by a Bugzilla ticket with the “wishlist” severity.
Context
Zooming out, I can understand that you’re frustrated that certain things you find to be important aren’t improving or being fixed as fast as you would prefer. That’s understandable. I get annoyed too when I encounter bugs.
But it’s important to zoom out even more and remember that KDE didn’t charge any money for any of this stuff; it truly is provided “as-is”. The whole thing is a gift we give away to the world for free. The facts that developers are willing to improve it for free in their spare time and then give away the results, and that companies are willing to put hundreds of thousands or millions of dollars into it and also accept that the results will be given away for free — are nothing short of modern miracles.
Now, does this mean we should be complacent and not care about improving it further? Of course not! But it does help to re-align expectations. I find that it helps to approach problems with a “how can I help?” attitude rather than a “why didn’t someone already fix this?” attitude.
A good way to start helping is to provide a clear description of what problems you’re facing. You already mentioned one bug report. That’s good! What about the others? Reporting bugs using bugzilla.kde.org is the first step, and being clear about which ones are important to you in communications here is the next one.
Beyond that, additional options include:
There are more too, these are just a few examples. But you are not a number, a faceless user with no agency, or an annoyance to be ignored! In a project as small personnel-wise as KDE is relative to its impact, every person matters.