Rigid adherence to certain technologies could be a culprit. "We're a Ruby shop!" is fine for problems where Ruby is great, but the limitations of the technology are bound to creep up somewhere. Not using a polyglot approach would be bad.
It can also be caused by too much embrace of polyglot tools. "We use the best tools for the job" can easily mean an architecture with Redis, Memcached, Mongo, MySQL, Angular, JQuery, Node, and several dozen third-party libraries, all glued together with Thrift or JSON-RPC. If all you're doing is a messaging app, you might be much better off with a single in-process Java app.
Usually you want your solution to be just right for the problem; solve the essential complexity but don't introduce any accidental complexity.
