Win9x classic theme, XP's Luna theme, Vista/Win7 glass theme, iOS 1-6 theme were all so nice. I can also live with iOS7+ theme and actually quite like Android 5+ material theme.
Older UI themes were often done by real experts. XP's Luna theme was done by Frog Design.
Some newer designs seems like be done as an afterthought, "designed" by an color blind programmer.
Today webapps take forever to start and are severely limited.
We'll start with the stereotype/assumption that many engineers prefer stability and consistency in many aspects of their environments.
April Fool's day upends consistency in a significant fraction of consistent events and assumptions. The corollary is that the only consistency introduced on this day alone is the inconsistencies introduced elsewhere, and even this isn't certain given that not everyone participates.
Therefore, if many engineers strongly prefer consistency and April Fool's Day disrupts consistency, it potentially stands to reason that many engineers do not prefer to be involved in/with April Fool's Day.
...I'm less of an engineer and more of a manager now, so I've come to appreciate the gags, but man was there a time when I didn't. lol