Why can't I see more than one page of threads?

If you do that you have to involve a lot of cursor positioning; which you have to do anyway if you are reading out the current page navigation set. People also like to have First and Last links as well as a way to jump up and down a couple of pages at a time i.e. full pagnation. The only way to offer that functionality is to know the number of pages that have to be generated, which is n = threads/30.

That functionality is available, but you have to click to get it - and that request is stored in the session cookie so you only need to click it once per session.

Yes, that is much lighter on the database load, I do not disagree.
You have changed what you were asking for, initially you wanted page number hyperlinks, now you are only asking for the next/previous pages here. The 'View previous/View next" thread imediately above this quick edit box are assigned that way.

I shall give it some consideration as it is a good idea and does present a way out of the current google problem - but it wont happen before Christmas at the earliest.