Why do the inserts in pasta pots not go all the way to the bottom? I love using a pasta pot/steamer where there is an inner "colander" pot so that you can pull all the pasta out easily.

BUT... in all of the ones I've seen, the inner colander doesn't go all the way to the bottom. There is a gap of about 1.5 to 2", plus the 1/4 space of the bottom of colander itself.

The means I have to boil a LOT more water. That takes more time, uses more water and energy.

It seems like a gap of just 1/2" or so would be sufficient to "insulate" the bottom of the pasta from the hot bottom of the pan. (And I've boiled pasta for years without a colander inside (so zero gap) fine).
You might have given the answer in your question.  If the device is to be used as a steamer as well, then there has to be enough room at the bottom of the pot for steaming.  How much is enough?  There are two things to consider:


The bottom section should hold enough liquid that there won't be concerns about boiling the pot dry for anything you might want to steam.  Longer steam items might include mussels, lobster, or tamales.
There should be some 'air margin' for foods like tamales or broccoli, so that the boil splatter doesn't render the food soggy.


Based on FuzzyChef's comment, it sounds like there are tools that suit your needs better.  Perhaps it's time to put your steamer on Craigslist? :)