I'm not sure what you mean by 'all at once', since rather obviously not all of those lines of code are running at once. The 'S' in SLOC does not stand for simultaneous.
The application has been continuously developed for nearly 10 years now, and small parts of the current codebase are 5 years old. A little while ago, I was very pleased to find and remove some code that was weird in order to work in IE4, but these days I'm enjoying removing IE6 and IE7 specific code. IE8 is the last non es5 browser we have to support and it's painful. The whole application runs in the browser, and connects to services it needs via streaming connections.
Once you take into account the fact that it's not just a couple of pretty forms for a back end application, plus the fact that in the browser you have to write things that come as standard in many other environments, plus the fact that you used to have to write extra code to work on different browsers, plus the fact that the javascript ecosystem was not up to the task back then so lots of things that would be generic now had to be written in house, plus the fact that it's extremely well tested both with unit tests, acceptance tests and integration tests, then a large codebase is really not all that surprising.
The application has been continuously developed for nearly 10 years now, and small parts of the current codebase are 5 years old. A little while ago, I was very pleased to find and remove some code that was weird in order to work in IE4, but these days I'm enjoying removing IE6 and IE7 specific code. IE8 is the last non es5 browser we have to support and it's painful. The whole application runs in the browser, and connects to services it needs via streaming connections.
Once you take into account the fact that it's not just a couple of pretty forms for a back end application, plus the fact that in the browser you have to write things that come as standard in many other environments, plus the fact that you used to have to write extra code to work on different browsers, plus the fact that the javascript ecosystem was not up to the task back then so lots of things that would be generic now had to be written in house, plus the fact that it's extremely well tested both with unit tests, acceptance tests and integration tests, then a large codebase is really not all that surprising.