What makes it feel worth it
A yearbook feels worth it when it captures the people, events, and memories you would actually want to look back on later.
If the book feels generic or too school-wide to feel personal, that is usually where the value starts to fall off.
Why people make their own instead
A personal yearbook puts your own pictures first. It is often cheaper to start, easier to control, and more likely to feel like something you made for yourself instead of something you were told to buy.
That does not mean everybody should skip the school book. It just means the personal option is real.