Dear Troy,
I personally believe the "tank meta" is nothing but an illusion. I've played on/off over the years and have noticed that tanks were on/off in terms of being viable. This point in time sees tanks "on" in what may be their biggest spike in power which has simply made them as viable as marksmen. Because tanks are now as seemingly common ( or close to it ) as marksmen people claim of a meta that does not exist.
Moving on from the so-called "tank meta" I'd like to ask if you let your team mates know about your engages in advance. If I'm on a team and I have a potentially powerful skill ( Sion and Zilean both have very powerful ults ) I make sure to let teams know in the game lobby that I have X skill, what it does and how to best follow up. Then, if I'm in a game with Sion and am about to ult I let people know I'm going to use the ult ( and if I'm rushing into an enemy tower that I'll be using my
if I built one ) and that they should dive if I manage to stun foes. If I'm in a game with Zilean I let people know when my ultimate is off cooldown and that I'll be able to ult ( his ult restores X flat HP +200% ability power to a downed friend ) somebody in the next fight. Since I began doing this I've noticed my teams have had a much easier time following up or setting up for my actions.
While it is true a lot of people leave tanks high/dry ( possibly because people think they can escape bad situations because of their high health ) and neglect to mention when they are or not going in we as team mates are also responsible to do the same thing and ASK for communication when we are not getting it. If I find my team is not talking/communicating with me I tend to do a lot worse and thus begin asking ( and sometimes begging ) for communication. A lot of the time the team will begin communication if each individual knows they are valued and needed in order to win. In the event no communication or flaming begins as a result of you seeking communication then you may want to toss a surrender vote out to see if the team feels like continuing the game.
TL;DR: Explain what you feel your key abilities are/what they do before the game begins and let people know when you are going to use them or when they can be used/expected. Ask your team for communication and let them know that they/their communication are important factors in winning the game.
Best regards,
Mr. Beane.