Mastery Pages

I know this isn't something that gets brought up often, so I'm going to. But this is pretty much a simple question. Why are we limited to 20 Mastery pages?

There are 123 champions in league of legends, and to get out of most of them you have to take a really specific set of masteries and runes. Most champions seem to share similar if not the exact same Rune set ups, so with 5-9 I'm pretty sure you can fit a lot of champions. But mastery pages are typically very diverse. I do run into a few champs that use the same mastery set-ups, but most of the time it's something wildly distinct.

Anyhow, is there any possible way we can get a few more? Now that I own more champions I find myself unable to play some to their best, since I'm missing a mastery page that functions well with them. Most of the time I'll use what I think would fit the bill best, but it still probably isn't the best. It'd be a whole lot easier if I could just make more mastery pages.