All but one of my capped characters has a greensteel accessory (and the only characdter I have ever TR'd is my cleric). Because greensteel is crafted, its where I put necessary item attributes that didn't fit in with the other epic gear. Only rarely does this involve HP bonuses (and usually just +10 if it does). More likely it is greater fire resistance, deathblock, fear immunity, or charisma skills (for UMD, +6) combined with 150 spell points. That's because those are things that actually provide increased survivability, which is what the noobs don't understand.
I can count the damage sources that do more than 400 damage to a player character in a single strike on one hand, and the one-shot abilities put in this game are FAR in excess of what they should be. Games like this have ALWAYS been about either avoiding damage in the first place, or healing. Unfortunately, the developers have decided it should mostly be the latter. That doesn't mean, however, that you need a big hit point pool (that will just make your team fail)...
...it means you need to be able to HEAL.
Because TR = Con being a dump stat since they're so awesome now and have such kewl gear that they no longer need the extra HP
Answer to the OP's question: because some people give tiny rats ass about hp and can complete quests without floaties.
Since I'm on like my 30th life I enjoy a challenge when I play my alts, I try different things. I have done dump stat con melee rogues, I have done the HP heavy barbs.
For me having low hp adds a bit of challenge especially when I also dump AC, not like that even means anything anymore.
Nothing is more fun then bringing a melee alt into epic elite with 220 HP.