More lines == better readability, better debugging, easier to move around, easier to fix single parts and so on.Disagree. There's a sweet spot. Code that is too dense (golfing code) is unreadable but so is code that's too long. Long code can be readable if the substructure is evident, but it's usually not.
There are two issues that come to mind on this. One is that concise code usually requires strong familiarity with the language. For example, Haskell allows dense and readable code-- if you know Haskell. Same with Clojure (Lisp). I hate Java, but one thing I'll say for it and its sprawling code is that it's relatively easy to (superficially?) understand (with an IDE to jump around, because modest programs can be thousands of lines) with a mediocre knowledge of the language.
I'd say the same of research-level mathematics. If you're intimately familiar with linear algebra notation and terminology because you use it every day, it's concise and readable. If not, then "(X^TX)^(-1)Xy" looks like line noise.
The second issue is that what tends to make large codebases unreadable is a failure of factoring. It's not that it's 500 lines* that is the problem, because the intrinsic complexity of the problem may be at a level where 400-500 lines is appropriate. It's when you have 500 lines in one class (ultimately, "class" and "object" are poorly-defined and that's why so much OOP code is trash) or, worse yet, one function/method (method is just a code-name for "locally interpreted stateful function") that you get hell code. This happens a lot in large imperative codebases (typically not becoming intractable until you have two or more programmers on the same code) because, in imperative code where an action (as opposed to stateless function) is the fundamental unit, things appear to compose better than they actually do.
In other words, it's complicated. In general, there seems to be a density level that accurately represents the intrinsic complexity of the problem. Go denser and you're forcing people to think in a specific (and poorly communicated) way to understand the implicit structure and policies that informed the code construction. On the other hand, typical sprawling Java code is great for testing your IDE's scrolling feature but the amount that can fit on a single page is low, and if this is coupled with long methods and huge classes, you get OOP (here, meaning "business OOP", not "Alan Kay's vision of OOP") spaghetti code.