I suspect it is based for quick, easy, user customisable layout and touch, with average fingers… for IoT purposes, not a paint program 
You can tailor Widget color choices via code to … well I don’t know the limit off the top of my head, 256K or 16 million??
EDIT - with 256 levels per channel, I believe it is classed as True Colour (24-bit), thus 16 million, but I haven’t counted them all yet…
Blynk.setProperty(vPin, “property”, value)
A good example of the variety pf colour options is here… (not just LED… any widget that has color option).
Again, probably for the simplicity for scaling and its primary purpose IoT, not word processing 
Only for the vertical Slider… and understandable due its width… who wants to tilt their head to read a sideways label.
And besides, Blynk is in constant development and there are reportedly lots of changes coming, including some UI stuff apparently… 