As much as I like Sinatra, there were some limitations I found frustrating and unnecessary when using it in the real-world. These were mainly issues of code management and scalability. You either had to put all your routes for your entire application in a single "controller", in which they shared helpers, filters, configuration, and so on, or otherwise try and break your application out into multiple mini Sinatra applications, and mount them under different mappings using Rack. Neither solution was elegant. I thought Padrino might address a few of those issues, but found it equally if not more frustrating.
Given that I had a pretty good idea of what I wanted and because it was simple enough (maybe not in hindsight), I decided to roll my own, knowing that I'd not only be scratching my itch, but the itches of many other developers who inadvertantly run into issues of practicaility when using Sinatra.