Supports get most of their money from assists. If your adc can't provide those, you are f**ked.
_"When a champion is killed, the main killer gets a certain amount of gold, while 50% of that amount is divided up among everyone who got an assist on it. _
If a player has 2 more assists than kills they earn 30 additional gold for their next assist. If they have 3 more, it's 45, and 4 more assists than kills reaches the bonus cap of 60 extra gold. This bonus cannot be more than the original value of the kill. "
That's how it goes. The more you have assists (than kills), the more you get money.
In my opinion this is kinda bad for the losing side supports. It means that if you don't get any assists you will not get the necessary money income for your support items and you will be almost useless.
I think it would be better if some of the **extra gold from assists **were moved to support item gold generation to give more balanced income between the supports.
The gold difference between a support with 20 assists and a support with 4 assists is huge. That is 1k extra gold in their pocket, on top of the original gold granted from the assists.