Back then you could put points into a little bit of everything. You could get some sustain, mobility, vision control and damage all in the same page if you wanted. Or you could go for only one of those and a bit of something else. Nowadays with Runes Reforged most of the runes are just ‘more damage’ and are so linear. You can only go for sustain, or damage, or tankiness, or DoT and a tiny bit of something else. You can’t go for more than that anymore.
Another bonus was that since you could have 20 pages, you didn’t have to change your masteries every time you wanted to get into a game. Make League of Legends great again, and bring back the masteries from season 5, where there was a time before keystones. A time where assassins actually had to land their combo to one-shot you, and while champions with lots of poke didn’t get random extra damage from Arcane Comet.