Before the pandemic, you could have purchased a PSA 1 example for around $10,000 USD and now it's worth around $40,000 USD, and that's around a 4x price increase in a short period of time. But a PSA 4 has only doubled in value. For example, if you had spent $30,000 USD on one before the pandemic, then today it's worth around $60,000 USD or so.
If you had spent $100,000 USD on a PSA 6 before the pandemic, well now it's worth ... wait for it ... about the same price! 
Does that make any sense to you? You would think that if an ugly PSA 1 has gone up 4x, then a PSA 6 or a PSA 7 should be worth $400,000 - $600,000 USD, right? But nope, that's not how it works! The real winners here are those who kept their ugly ones, and of course, those who bought this card in PSA 8 (or higher) prior to the pandemic.