They wanted more realism and the problem is, you have a fanbase coming from very fantasy type gameplay. Grab a bmx, a jetpack, etc. Roads are open and sparse because of the hardware limitations etc. .
I'm really tired of the false dichotomy between people who like "realism" and people who like "fantasy gameplay with jetpacks," in regard to GTAIV. Wanting a highway in the game (highways are realistic by the way, they exist in real life and in New York) does not mean you want jetpacks.
There are some sections in IV with straight up bad level design, based around roads, and that doesn't make it more or less realistic, just bad. That one section off of the highway in Dukes is classic. 80% of the time you're driving to Dukes you're headed towards Joliet Street, where your safe house is and a number of story missions, but that highway goes from a 2 lane freeway down to a small exit ramp at the end of the freeway, and then you have to take a full U-Turn at the end of that corner, where there is a traffic light...
Here:
You have to do this dozens of times, and a handful of times there's a cop who's going slow at that bend. Also, you're coming from the toll booth area so you have a high likelihood that you're already being chased by cops (I don't mind the toll booth thing, I think it's unnecessary but I don't hate it -- I only hated it when there were 2+ cars in front of me and every time, the 2nd car would fuck up and you'd never be able to get through it without breaking the law). The bottleneck, the very narrow 1 and 2 lane street (1 lane exit, 2 lane road you need to cut onto), and that you're going down a hill that banks to the right makes it very difficult to NOT crash here or inadvertently run over a pedestrian.
The game is filled with sections like this where there are speed bottlenecks for no reason... But the Dukes bottleneck is the best example. They didn't have to build it like that. It doesn't make it more or less realistic, it just makes it lousy and annoying.
I'll also say that having a highway that weaves into the major bridges is also not unrealistic... In fact, New York has several of them in real life. There are no stretches to get any sort of speed in the game, other than perhaps that one U-loop around where the Lost and the Damned was set, which was unfortunately a highway to nowhere that served no purpose (you entered right next to where you exited and just did a big loop over the industrial portions).
I'm not somebody who likes 'unrealism' over realism, or who 'wants jetpacks,' and I don't think that wanting good road design and a highway -- two realistic things -- means that you want jetpacks or a fantasy environment. Thankfully, from the previews of GTA5, it looks like Rockstar is on the same page.