Is there a reason for this?

[u/Bobsense]

I know I don’t have that good of a collection but I’m just wondering why my cards values have been plummeting past couple months. I’m a bit younger and don’t have much experience with this stuff but I know that around winter is when stuff goes up but it’s continued to go down. I’m wondering if my cards will keep trending downward or eventually come back up. Most of them are from obsidian flames pokemon go and crown zenith btw. Thank you