Simple answer: they need to make money to exist as a community. Without you paying, they don't get any money and the company shuts down, no more League of Legends. So, if you really do like to play this game you might think about spending a tiny bit of money on it so it can keep existing.
More complex answer: If you watch Phreak's twitch channel, he did a very good job on explaining runes and masteries and how to optimize them. He uses "18" of his 20 rune pages, but in all reality he even states that you really only need 2, maybe 3 max to be competitive. If you look at a lot of the pro player's smurf accounts they don't have 20 rune pages, they have 2 or 3. You don't NEED specialized rune pages. Personally, I only use 4 of my 11 rune pages consistently and some of the differences between my rune pages are only scaling/flat stats for matchups that are difficult. People think you "need" a full 20 rune pages, and I did too, until you really think about what you need in a rune page and a basic AD page (AS, AD, armor, MR/lvl) a basic AP page (AP, magic pen, armor, MR) and that will cover almost every single champion in the game. The third if you really want to be specific would be a "full" tank page of (armor, armor, hp/lvl, MR), but almost every tank wants AD to either help csing or jungle clear so the first 2 pages clears almost every champion in the game. There are optimizations you can run for certain champions like switching the AS quints for lifesteal on a Nasus or getting armor pen for assassins and running flat AD instead of AS, but still you really don't "NEED" lots of rune pages, it's really not that bad. Heck, I only have 10 mastery pages and that covers almost every champion I run too. Basic pages work for almost every champion with very few changes for optimization.
tl;dr: You don't need more than 3 rune pages, just learn how to make blanket pages and you'll be fine. The only time you "need" more rune pages is for really really tiny modifications that really won't make a game-changing difference