In my layman's opinion it's partly specific issues with how Madden is fundamentally designed and partly Tiburon intentionally not doing things other games have done in Madden.
To the first part, if you read back at old threads when OS members like LBz, Bezo, PGaither, AJ, etc were going down to Tiburon for Community Days, they mention quite a bit about finding out/being told why x couldn't be easily done in Madden, unlike in other games. Also Ian touches on it quite a bit in his post Tiburon interviews. A general theme that seems to come up is Madden is a mass/mess of code with all kinds of things, linked to other things, so doing some of the seemingly simplest things, ie scaling the size of the actual football, can be like doing brain surgery for Madden. For example, those CD guys had been asking about things like tiered play calling and route based passing for years but that's difficult because in Madden the olne/dline are programmed together as a unit, as well as seemingly the receiver/defender/ball. For quite awhile there were even sliders and settings Tiburon didn't want Users accessing in Madden because they claimed they could "break" the game.
So considering that, in addition to the way we can often see a pursuing defender 10-20 yards away from a play still reacting to a ball carrier's evasive moves, sometimes multiple defenders mirroring each others reactions and the dreaded "Conga line" pursuit, it's likely defenders and ball carriers movements are all somehow linked in Madden's "unique" design.
To the second part, I don't think much, if any, of that applies to things outside of game play coding/design, considering areas like presentation, commentary, and career modes are separate teams and have been ripped out, rebuilt, ripped out, rebuilt again, seemingly numerous times. So when I see FIFA's living World, FIFA's multiple commentary teams, HC09's team management, NCAA basketball 10's presentation, etc, more fleshed out than what's currently in Madden, I see those areas as being intentionally designed not to match those other games. No way I believe they couldn't have ripped out Franchise mode from M12 and completely replaced it with a better version of HC09, instead of CCM/CFM. However they decided CCM/CFM was the way they wanted to go, that's not legacy coding issues, imo, that's choosing to offer something else other than what's already been/being done.