SEDO or any other parking company has no benefit of hindering your domain's traffic, quite the contrary
imo, you chose the wrong place to park your domain. try some other places like Voodoo, parkingcrew, bodis, etc.
SEDO has bad support and an even worse interface. I don't remember the last time I got a non-bot answer from one of their support people
Now, as for your traffic
There are various reasons why you stopped getting uniques and clicks.
One of the most common ones is that you acquired a domain that the previous owner had paid traffic on which obviously stopped since the domain got dropped.
Another reason could be various testing bots. I once had a newly registered domain (newly as it was never registered before) which suddenly got hundreds of visits and occasional clicks from china.
That stopped as abruptly as it started.
As a final note,
you can always have domains posted on different marketplaces and have them parked elsewhere. No one stops you from having a page that you choose on your domain but at the same time sell it via your favourite marketplace.
All the above parking places I suggested provide redirection links via the parking page to send the potential buyer to a marketplace (or an escrow) that you choose
if you want an example, please open a conversation with me and I will link you one of my domains to see how it looks like