As Tank, you have to take the lead role in every dungeon. Tanks get kicked out because they are not prepared for new dungeons (= not knowing what to do) or undergeared. Of course not all the time, because there are many other people in dungeons who can help out with tips and tricks, but overall i can just suggest you to watch a video guide on youtube for every new dungeon, so you can prepare yourself and know what to do in specific moments during boss fights in that dungeon. I know that this is might be something you dont want to do, because it seems you only want to play the solo part of the game, but the 4-man dungeons are a very important content in the game. They simply teach every player how to do well in thier specific role and to be prepared for end game content once they completed the main story.

So yeah, as tank you did choose the hardest class in this game. Your only option is to watch guides before you enter a new dungeon.

Edit: Some dungeons are also a heavy difficulty spike, like brayflox.