Camtasia is just really polished and optimized for screencast videos.
There's so many little UI enhancements to make the process of editing video feel really good and not buggy.
It's also extremely easy to make complex animations by just clicking 1 or 2 buttons and dragging a couple sliders[0], along with it being very easy to add great looking text overlays, tooltips, zoom / pans, transitions, blurs / highlights, etc..
Most of these things aren't possible to do in kdenlive or any other editor on Linux and it's not just a matter of "get used to the UI of the new app man!". I tried for hours. I actually spent full days (actual days) playing with a bunch of them. None of them are even comparable. Things are either really hard to do (ie. they take 5 minutes to do instead of 5 seconds) and there's so many UI bugs. It's just not an enjoyable or productive environment.
I would go as far as saying having a non-optimal video editor is even worse than having a non-optimal code editor. For the record I've recorded hundreds of screencasts and put in 100+ hours of editing video.
[0]: https://www.youtube.com/watch?v=XeSD17YRijk , This video was made entirely in Camtasia but the first 10 seconds of that video was also done in Camtasia too. I'm hardly an animation expert but that took seriously only minutes to implement by dragging a couple of sliders around without really knowing what anything did. I tried to replicate it in kdenlive for an entire day and didn't even come close to being able to do that.
