Well, the basic idea is that if you have enough HP to take the big hits (tank busters, for example), then there's no reason to stack VIT. Extra VIT will just net you extra health, which means the healers have to heal you for more to keep you topped off.

It also is bad for Living Dead, where you need to be healed for 100% of your HP (the more HP, the harder the healing check). Then you also get to abilities like Souleater, which heal you based on the damage you do. This means that stacking some STR accessories will allow for better self healing.

Then of course, the most obvious reasons would be for the extra DPS and keeping aggro. So in my opinion, if you can take the hits, there's no need to keep stacking VIT. Just wasted points honestly.