Also, for many modern comics (well many comics in general), grading them s only worthwhile if they come back 9.8.
Here's an example, a dealer friend of mine had lots of Firestorm vol 2 #1 that looked really nice. He thought like you, why let money on the table when a 9.8 could get back way more than selling raw. So he sent them in. They came back 9.4 and 9.6. With the time and money spent on grading, shipping, pressing, that was a loss for him. He would have made more simply selling them 10$-20$ raw. That same scenario can apply for most books, showing you why dealers won't have all their books graded.