"They should"? "We are demanding"? Whatever they do, whatever they release, whatever they use, however it is based on or forked from Linux, nobody can "tell anyone what they should do" - unless he pays them to do it. And nobody can "demand" anything from anyone, unless, whoa, see, same thing again, he pays for it.
GIMP is "evolving" for the better part of the last 15 years (count them) and it still sucks. Same goes for most of available open source software, with some major exceptions - from Apache to Squid and from WordPress to MySQL.
Let's say that Google releases a Linux compatible version of Web Designer. With what are you going to use it? "Pure code"? With what are you going to design vector and bitmap graphics to use in your designs? Inkscape? GIMP? Linux doesn't have 99 of the freakin' 100 tools needed for graphics and multimedia, yet here are the Linux zealots, crying that THIS is what was missing from the puzzle.
Well, if that makes you feel better, from the little I've seen (I may be mistaken), Web Designer creates what's called "dirty" code. Not-so-optimized and more bloated than any serious web developer would like. Apart from that, it's almost exclusively useful for creating animated banners - not sites, not pages, not any other "general use". It's too complicated for anything other than ads (not meaning "I don't get it", but "needlessly complicated for stuff like creating a simple menu"), and thus, useless for anyone wanting to "simply design a static banner or a design for a site/blog". There are better tools for that.
So, all Linux fanatics are crying that Google hasn't released its new HTML5-CSS3 animated banner creation tool on their platform, when they've got everything else solved.
And before any moron cries "fanboy", yes, I'm working in Windows. I'm also looking at my Linux boxes for the better part of the last 15 years, not finding anything useful to do on them apart from setting up servers, download boxes and learning some programming. There aren't any serious tools for graphics (compared to other platforms), video (compared to other platforms), music... Heck, there's not even a file manager like Directory Opus (no, don't tell me "there is" if you haven't worked with Directory Opus "because it looks like the ones you use" - I've used them all, and compared to it, they're like Notepad compared to Vi).
So, why don't all Linux fanboys go cry up Adobes alley, or try to create ONE tool that doesn't suck (compared to what's available to other platforms) instead of constantly copying and forking the same damn things, then demanding from others to create something that actually works?