Why does gulp run tasks more slowly as it runs?

Question

css

Actually, the question is why gulp.js performs the same task more and more slowly as it works.
An example of a task execution in a GIF (sorry if the scroll is too fast)
Attention to the "styles:dev" task, at first it runs in less than a second, after two hours the execution time increased to 9s, why? the files themselves that it processes do not change much. And if you just exit the execution of the 'watch' task that automates this whole thing, and start it over again, the execution time becomes normal, fast (up to a second), and again over a new one after two hours already 6-9 seconds.
here are the tasks from gulpfile.js

Answer 1

The problem turned out to be in the watch task, namely watch on html files.
I chose html files for tracking like this: 'src/**/*.html'
It turned out that you can't specify that, xs why. Changed in my case to ['src/*.html', 'src/templates/*.html'], now everything is fine.
To be honest, I didn’t understand what kind of magic, and I’m unlikely to understand, if anyone knows why, I’ll be grateful.