Gw2 is to complicated that auto-group could work for harder group content. You need have healer, but you need also buffs, most important quickness and alacrity, but your healer can provide only quickness for example HFB, or Herald or alacrity as hMech or hTempest or Druid. So you need option in auto group for what kind of healer are you and then what kind of boon support are you. But some encounters need tanks too, like some raid wings but others don't, you don't have tank for example in wing 2. So auto grouping would need consider that somehow. But there is more, some raids need specific roles, you need hand-kiter for Deimos, you won't kill it if you don't have that specific role, or you need specific dps that can do pylons in wing 7, or people who do greens on Dhuum... It is impossible that auto groups would consider all that.