Second Letter of Invitation

Passports are a funny thing. The come with a specific amount of pages, but one could get more pages inserted if they wanted to. Why wouldn't the issuing country just include those extra pages and assume, since Passports are valid for so long, that people would use them. Traveling in this part of the world, I lose a page almost every time I leave the country, and in some cases, I lose 2 pages.

For travel to Saudi Arabia, the Visa takes up a page and then the second page has to be free for stamps from Bahrain, as that is where I land and drive into Dammam from, and for stamps entering and exiting Saudi.

So, why don't they just include the extra pages when you get your passport? Why do they insist that I go back to them, or to a local embassy, in order to add pages when I run out?