I'm probably responding more to this thread than I should, but I'm an a chatty mood today :-) I think there are a lot of factors and this is almost certainly one of them. Having worked in a couple big, wealthy and famous companies before, one of the biggest problems is that they are always making acquisitions. One day you're building X and then upper management thinks, "Woah... X + Y would be awesome. But we don't want to spend time to build the Y part. Let's acquire a company and glue it onto X." Usually that happens with great grumbling from the programmers who complain that X and Y were never meant to work together and it would actually take more time to get them to work well than it would have to build Y in the first place. Upper management doesn't believe this and says, "Stop grumbling". And, well, the programmers do what they have to do. So it ends up being super hacky... because it is super hacky :-)

But I think it's more than that. You know how certain things are obviously built by committees? You can see it because everything is consistent, but it's often got a lot of compromises. On the other hand some things are obviously built by individual contributors. It's got some things that are really great, but other things that are horrible because the developer just has blinders on. Many Google apps give me the latter experience. Also, when they have a suite of tools, although they are tied in together, they have wildly different UI, naming conventions, placement and layout of information, etc. Usually there are some really cool bits, but these bits are often not the point of the project and look a bit out of place.

I think teams in Google often have people who are confident and smart and the tools reflect that. It's a kind of "This is the way to do X", shouted 500 different ways. One of the biggest things I find frustrating is the mountain of trivia that I have to commit to memory in order to use their tools fluently. I really do think it reflects the type of people that Google chooses when they hire people. While they may be good at the things that Google screens them for, they may not be the best people overall when it comes to building finished products.