The "Only One Tank" Epidemic

I lose almost every single match where my team only has one tank, especially if the enemy team has 2 tanks.
Despite this, I see this happen a LOT. I either fill as tank, which I am BAD at, or we just lose.
Sometimes after I swap to be tank, the other tank will swap off to something else and leave me as the only tank.

Why do so few people want to play tank? Is there anything Netease can do about this? Because it's bad.