The site is so biased, that a lot of people expect the PS5 to sell less than the PS4, even if Sony themselves said they expect PS5 shipments to surpass PS4 shipments (launch aligned) in 2023.
I'm sure many of them have had a look at the statistics and see that the chances that the PS5 outselling the PS4 would break some established trends.
Playstation + Xbox sales taken together have always amounted to ~175M each gen:
- PS2+Xbox: 183M
- PS3+360: 173M
- PS4+XBO: 168M
Meaning if the Xbox is stronger, then the Playstation sells less as a result. Since the XS is selling much better than it's direct predecessor, unless this gen breaks with the model it established the 3 previous generations, PS5 should sell less than the PS4 did.
That being said, there are some unknowns that could alter this a bit: How long this generation will be can have an effect for instance, if there will be some mid-gen upgrades like the PS4 Pro last gen, and so on. So far, noting shows that this gen will deviate from the previous generations, but time will tell if this will stay the same.
Another thing to note is that the Playstation + Xbox total has been dropping a bit each generation. This trend will have to be reversed for there to be any chance for the PS5 to outsell the PS4 since the XS will almost certainly outsell the XBO.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/