There is not an infinite amount of raw 9.8 copies...of any book...in existence, nor is there an infinite amount of lower grade books that can be pressed up to 9.8 (or any other grade, really.)
We are now in, and have been for a while, the era of diminishing new census numbers, especially for heavily traded books like Hulk #181. In the 00s, the census was filling out, and people didn't really have a good idea about what was out there, which is why people paid such premiums for "highest graded books."
That's no longer true.
The era of the census doubling, tripling, quadrupling, or more is essentially over, for most of the "key" books. Yes, there will continue to be a steady trickle of new census entries, as people sell their previously raw copies, or books get resubbed without turning in the old cert, but it would be quite the miracle if the number of Hulk #181s on the census even tripled in the next 20 years at this point. It's certainly not going to go up tenfold as it did between 2001 and 2013, or double again from 2013 to now. And while the rate of submission has seen an uptick in the last 2-3 years, again...there aren't an infinite amount of copies out there raw. Yes, there are a few people who have a decent amount of raw copies...but that number probably isn't "thousands", even over the entire world. That is, while there are certainly a couple of tens of thousands of copies still raw worldwide, there probably are only a handful of people who own multiple copies, not counting dealer inventory. Maybe 20-50. And of those tens of thousands of raw copies, probably less than 100-200 can lay legitimate claim to eventually ending up in 9.8 slabs.
NOW the era we are in is "this is how many are on the census, this is how many are available, now let's see where the demand really lies." Now we get a more true picture of the value of these books in their various grades, as opposed to the false values we got in the mid to late 00s because of the artificiality of the census. This is when the real fun starts.