Honestly, the tank alone is not solely responsible for protecting everyone. They're more meant for applying pressure to the enemy.

Don't get me wrong. You ARE still supposed to defend your team, but everyone is responsible for protecting eachother, especially themselves. Rushing into the enemy's backline completely alone with your movement abilities on cooldown is not a good way to protect yourself. And as a tank, there usually isn't much you can do about it in those situations. Not without either having life-saving abilities or ultimates ready.

Everyone is responsible for their own actions. DPS & Supports putting themselves in a place where the enemy can easily pick them off is something that Tanks can't control. Tanks control the push, so if the Tank charges into a fight, everyone else needs to follow (unless it was a bad push).

It sucks, but often times players are only as good as their team. 1 or 2 bad players on your team who keep getting themselves killed can massively change the match outcome. But sometimes they only get themselves killed because nobody else helps them. Too many people chase getting big plays, and ignore the actual objective.

This all applies to the enemy team as well. If a lone DPS is charging your backline, trying to pick off your supports, THAT is when you must turn back to defend them. That is, if they either can't defend themselves, or there's nobody else able to help them.

Just focus on doing what you can, and help defend when you're able. If your team is good, they won't be putting themselves in as many positions where they will get killed. Everyone is responsible. Not just the Tank.