Whenever someone gets started with retargeting they get obsessed with the size of their cookie pool. Often getting greedy and trying to show their ads to as many of those people as possible.
The truth is that after about 30 days, or 90 days max, if the viewer has not bought, then it's very unlikely they'll buy. Your ads are now creating wasted ad spend plus aggravated viewers.
Remember, it's not about how many times you can show your ads and how many you can show them too, it's about trying to get them back and take the next step.
Smaller, more tightly relevant campaigns are almost always more profitable.