This question is surprisingly more complex than you'd think. The short answer is "we are working on it" but that's kind of a cop-out. The longer answer follows:
First and foremost, it is non-trivial to make any kind of changes to a top-five site that has such a consensus-driven community. And I mean every change, no matter how minor.
Wikipedia is not a privately held company. Larger sites (e.g., Facebook) can and do make radical interface changes without consulting the user-base but the reason that this is possible for them is precisely because they are privately held.
The Wikimedian community has a strong sense of ownership for the product, and rightly so: these are the people who write the articles. Thus, the community believes (correctly, in my opinion) that they should be consulted on changes to the interface.
This process takes a great deal of time. It is rather glacial in its nature.
That said, the Foundation has taken a position that allows it to make what we think are minor or important software changes as needed (such as deploying WikiLove, Feedback Dashboard, or the upcoming New Page Patrol interface). Mostly, these changes are subtle or invisible to "readers" (and most "editors").
Second, writing software is hard. You may think it isn't - especially if you have a passing history doing so - but you must understand that every Wikipedia feature must:
- Be able to be localized into over 370 languages. This is an enormous task.
- Be able to run on pretty much every browser ever made. Until the usage of IE 6 drops below .03% globally, we have to support it - which nearly always doubles development time. (We were only recently able to remove IE 5 for Macintosh from the support matrix)
- Be highly scalable. The Foundation has a shoestring budget. We do not have thousands and thousands of servers with which to generate every page; instead we make very smart use of caching systems.
- Be able to be used anonymously. The number of people who use the sites who do not have user accounts is astronomical. This limits our focus.
Third, we have fewer programmers. This is because of several reasons:
- We are a non-profit. As such we pay bottom-of-scale. It is difficult to attract programming talent when they can make 30% to 50% more money anywhere else.
- We prefer to employ the Free Culture-aligned. We prefer to hire people who are mission aligned or dedicated. A love of the work and what it stands for is extremely important to us.
- We prefer to think globally. You'd be surprised how difficult it is to develop things meant for a global audience. As such, we have determined that hiring from all cultures helps us to understand our weaknesses. We're not the best at this, mind you, but we're working on it.
That said, we are innovating, we're just doing it very slowly. Here are some projects you may be interested in: