As an example, Arthur and Ford are supposed to be friends, but from the interaction in the book, it seems more like they tolerate each other and don’t really appreciate each other’s presence or influence on their adventures. Every time they get out of touch, they don’t appear to feel sorry about it, and when they see each other again, they are extremely British about it. This also applies to the other characters in my opinion.
From the point of view of having lived 23 years in the UK: So what you're saying is that they're extremely close best friends who can hardly bear to be apart and get exceedingly emotional about it... in a very British way?
Arthur seems happy to just make sandwiches and doesn’t seem to mourn this loss too much after the initial search.
So you're saying he's British. He could be dying inside, and be expressing that by showing absolutely no sign of it and continuing to make sandwiches.
Yes, I'm exaggerating, but so was Adams, and the books were written at a time when this was if anything even more ingrained in British culture.
Also, these are light comedy books, and sci-fi on top of that, neither of which lends themselves to romance.
I've published a couple of novels (don't get excited - they've sold more than average, but the average novel only sells ~200 copies; I've sold in the 4 digits... low 4 digits...) and one reviewer complained the first one had too much romance. It had some tension. No dates, romantic moonlight walks, or even a quick stolen kiss. The second one had a kiss, and I keep wondering how angry that reviewer would've gotten about that. Point being that a certain segment of the key market demographics for sci-fi gets very irate if they have to endure anything resembling romance.
EDIT: Also, to it not having found this yet, just wait a few seconds and try the search button again, and repeat a couple of times if necessary. It usually shows up pretty quickly (but frankly the UI could do with better messaging on that...)
But it's very funny in a very British way that all of this happens, and everything is great and beautiful, and he then loses it all.
British comedy relishes the opportunity to totally pull the rug out under a character whenever they get too happy.
If there isn't an air of light despair about a character, surely that means there is pain and misery coming their way to fix that soon enough.
With respect to Mostly Harmless being bleak, consider that the first book starts with the destruction of the earth, and the deaths of everyone on it. "Less bleak" than Mostly Harmless isn't a happy ending, but one that doesn't so conclusively stomp on every possibility for happiness. Characters should have hope.
It just needs to be lightly stomped on with regularity to remind them that happiness is always temporary, but despair is forever.
But then Eoin Colfer's "And Another Thing..." did a decent job of showing that in a universe as crazy as Hitchikers, there's always another path.