From everything we have seen of Google's culture, working on new projects is exciting and is absolutely the way to get promoted.
Doing maintenance work, especially on products that aren't wildly successful gets you no attention, no staff, no funding, and probably more than a little tongue waging.
The CEO cant just change all that with directives, even if they do something extreme like a "No Depreciations" policy, products are liable to be depreciated in all but name (Joe the intern takes care of it every 5th Tuesday, technically not depreciated) by sheer corporate momentum alone, nobody wants to be stuck with a dead fish, even if its now illegal to openly comment on how much it stinks.
It would require change at every level of Google to place value into fixing/improving existing projects, rather than all the glory going to greenfield development.
Considering the kind of "kingmaker" culture Google's mentality breeds, ie what gets me ahead is gathering resources to focus on my project, changing things to a setup where contributing to other peoples silos is welcome and common is going to be an extremely difficult prospect because virtually all the people with power inside Google got that way by carefully tending their fiefdom, they aren't just going to throw that all a way, no matter what any executive says.