It's possible I've been thinking about Traveller all wrong. Maybe this is obvious to everyone else but here goes.
I've been reading some books about maritime cruising. "Living for extended time on a vessel (yacht) while traveling from place to place for pleasure. Cruising generally refers to trips of a few days or more, and can extend to round-the-world voyages." There's a lot of discussion about how to do your own maintenance (one, because stuff breaks at sea, and two because hiring professionals to do it in port is really expensive) and how to do odd jobs to make some money on the side since you probably aren't regularly employed. Some of those odd jobs and cruising stories sounded like the sort of things Traveller patrons would ask for, and here we are.
This lens makes a lot more sense for Traveller than "space trucking". You don't have to explain the economics of small-scale shipping, because that's not really what is happening here. Sure you might make a windfall on cargo every now and then (and cruisers attempt this too, with mixed success - "We were told that people in the Marquesas desperately needed reading glasses. I bought 50 pairs in Mexico and still have all of them [because we were misinformed].") but that's not why you're traveling. You're traveling for its own sake, and money is a means to the end of continuing to travel. You're not out to get rich - just to keep funding the midlife crisis and not have to go back to a day job with a boss and a commute. This is why your "career" ends at the end of chargen.
It's interesting to compare with the similarly non-accumulative style of Appendix N, where the heroes adventure to get rich, only to spend it all and then need to adventure again. Here too it's adventuring for money in order to maintain an unconventional, expensive but unencumbered lifestyle.
I think this view is consistent with the belief that money is supposed to be important in Traveller, but it also admits the Classic Traveller style where PCs having a ship is somewhat rare. A Traveller without a ship can still work odd jobs in / for the "cruising" community and get working passage to wherever. Losing the money game doesn't end the campaign; it just changes it temporarily. So the money pressure maybe shouldn't be as overwhelming as it might traditionally be with the starship loan (or you do what many budget cruisers do and get a really old vessel). It's there to keep things interesting, to add a creeping danger that you can't just run from, not to be the focus of play.
This cruising lens also answers the question of "why do we have a baronet or an ex-admiral on this grungy little vessel?" They're not loading cargo - they're just drifting. Plenty of nobles are into sailing ("It seems that of any activity in the world, singlehanded sailors have the best odds of being knighted.") and the admiral retired and decided he just wanted to kick back in the tropics in a low-stress environment but can't help but get himself into trouble.
Some possible implications for DMing Traveller - NPCs from the cruising community. Lots of cruising vessels have "buddy boats" or form regattas headed to the same place at the same time. This is good for when something goes wrong. The vessel at the next berth over in port isn't a rival small trader; they're drifting hippies with a hydroponic weed operation onboard, or a very trad religious husband who used to sell insurance with wife and four kids and a dog aboard, or a reclusive ex-programmer with a bunch of ship systems automated, or a husband/wife pair where the husband is a professional hunter and the wife is a xenobiologist (who is actually the better shot of the two), or... There's just a ton of room for recurring, charmingly-eccentric NPCs here, who might fill the patron role when things are going well for them, or who might need rescued when something goes wrong.
Another implication for DMing Traveller regards building sandboxes. When the players are out to do the "space trucking" thing, you have to be really careful to not set up Golden Pairs of planets with complementary economic tags where you can just go back and forth indefinitely and make tons of money. But if the players are on board with the game being about drifting, you might be able to be less careful with this; it becomes a "sometimes food", because anything that resembles routine work is anathema. It seems like a way of thinking about the game that would really encourage building a sandbox with lots of wild, interesting bits for your tourists to go see and mess with. It could be much mellower than the highly-incentivized OD&D sandbox of "where do we go to make a ton of money, hence XP, as quickly and safely as possible?" which so often causes analysis paralysis for optimizers (as does the Space Trucker optimizing his routes). But cruising Traveller admits satisficing; "sure that sounds like an interesting place to go, uhhh I wonder if they need any eyeglasses, maybe we can make a buck. Any passengers headed that way to defray our costs?"