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You don’t have to worry about one shots from widow or Hanzo, ever. Sure they’ll go for your team, but you can take riskier players knowing you won’t be deleted
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You can cancel or flat out tank most ultimates. Dva, Sigma, Orisa can eat or block most dps ults, rein can block, Zarya can cleanse, etc
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You have the ultimate with the most potential for team kills. That’s because most tank ults are for CCing or displacing the enemy so that your team gets the advantage, allowing for 1 ult team wipes
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You don’t really have to worry too much about picking off enemies yourself - your job is to make space (by literally taking it or by displacing the backline), and to peel for your team
I don’t think any of these upsides are unique to Tank. Positioning and routing helps with Widow and Hanzo.
Many supports can shut down ultimates entirely. Some DPS heroes have ways to shut down ultimates, not including just deleting the hero ulting.
Tanks have to be very careful about all their plays because the entire team at a minimum is keeping an eye on the tank, if not shooting them.
Tanks still need to worry about dealing damage and trying to pick off the enemy. They just also have multiple other jobs, some of which the player base just auto assumes the tank will do (peeling) even though it can be done by anyone. The change to 5v5 actually put pressure on the rest of the team, not just the solo tank, to also pick up the “off-tank” duties from OW1. The community is still learning this on the whole, especially lower ranks. Supports should be peeling for each other and DPS should also be helping in some scenarios. Too many people assume the tank is the only one that can peel.
The real upsides to playing tank, imo, are in the fun of the heroes kits and the variety. Also you are the typically the giant target so the enemy and your supps alike will tend to focus you. This can be quite exhilarating. Tanks have some of the most flashy and fun ultimates, even if they end up doing nothing sometimes. Also, Rein duels and Ball mirrors are a treat.