Tanks holding fights hostage in Roulettes

[Plumerian_Ariadust]

It is because the needs of the entire team need to be considered and not just the desires of one or two people

This is why Party Finders exist, you set expectations that everyone would be in agreement to not waste everyone's time.
Duty roulettes (except mentor roulette?) are there to fill bodies needed to clear content. Almost everyone there just wants their daily exp/tome/gil grind and want to be done with it.
You want to teach new players? that's fine, just don't expect that the others would have the same objective as you.

If someone is new, they most likely need the practice to learn how to not die on the mechanics.

Learning how not to die to the mechanics can be done by making a learning PF. (There's also an option to go in with NPCs)
Heck almost every mechanic in Valigarmanda is used and reused alot with some even used during solo duties.
Four Arrows converging on one player? stack, Big red glowy circle on tank? tank buster, serpentine boss doing a weird circling thing? inside safe spot.

[]If there are a lot of wipes and the tank doesn't want to help instruct or be there supporting them figuring it out (which they're not required to do) then they can take a penalty and let the party get in a tank who will be what the party need

If there are a lot of wipes, why not just [Vote Abandon] instead of having someone who queued for dailies leave and get a penalty.
If you are really inclined to help newbies, you'd reach out after the duty has been abandoned and teach them with a premade party that has the same goal.