Its not cool, just stop.
Most tanks that i find in pugs these days are endurance stacked sins or juggs with 10% defense and 40k health :/
Why do people think that this is good..
I agree that this is silly and a bit frustrating. Some reasons and further annoyances:
1) In most pugs, there's the assumption that the tank with higher HP is the main tank, and whether a tank is viable in a story mode pug (not a place that really matters, but still) is based on some sense of their number of HP.
2) Many players just have comm gear on, which has been high endurance junk. We are, however, now at the point where oriconian gear has enhancements that have more mitigation (by 1 point!) on them than the purple 66's you can craft, and hence have more mitigation than anything below underworld token gear. Still, tanks using all 69 or 72 comm enhancements are doing it wrong.
3) Many tanks (and even dps/healers) now don't have or want the arkanian armoring set bonus for some reason, despite it being better than 78 armorings and vastly better than 72 armorings. It's now crazily easy to obtain tokens because people shun them like the plague now that even elite comms give "higher level" gear. I think this is related to (1).
4) Many people don't know about the veracity ears and implants (which are only surpassed in total mitigation by the dread forged ones) and instead have some random terrible high endurance ears and implants.
5) There are damage spikes, which necessitates a certain level of HP (and more for sins currently, who also get a modest boost to their self healing from it). Still, this is really relevant only for newly minted tanks, and most go overboard by taking all comm enhancements instead of a mix if this is the concern, which just makes them take tons of damage in addition to spikes.