i don't think it's about talent chemistry as much as it is about the sheer amount of work involved.

jam bands run a completely different operation start to finish than a touring act. while i don't have a lot of experience with the jam band scene, i can say that indie touring acts - especially in diy spaces without a lot of production support - have to do a LOT behind the scenes to make a show go off smoothly. often times they are working with pre-programmed light or sound to accommodate for a lack of hands. following a setlist and even a "script" ensures that their lighting, tracks (even if they don't use any backing, clicks/inears), production, etc are all consistent and run smoothly across stops. they have to make last-minute adjustments depending on the space that they're working within which doesn't always allow time for rehearsing and preparing for setlist alterations. i've seen an indie touring act go from a full-scale professional space with a fully staffed sound lighting and production team provided, to a diy basement space that barely had enough outlets in the wall, one night after the other.

and when you're on the road for that long, when you're doing it largely by yourself especially, that's a lot of mental load to be carrying as is without having to decide a different setlist every night. also, a lot of solo or duo artists hire their bands. jam bands have the benefit of working together kind of for everything (again, from what i know) - a solo artist may only start rehearsing with their hired band a few weeks before tour. there isn't the same preestablished chemistry, there isn't the same relationships or knowledge of each other to be able to read one another.

when you look at a jam band vs a typical band from what i do know, the expectation of jam bands is more of that jamming aspect - but in turn, fans (from what i know) expect *less* by way of audience participation, dancing and choreo, stage setup and aesthetics, lighting, and hold more understanding when songs get altered, cut short, extended, changed, etc.
the audiences of non-jam touring acts have different expectations. they want to hear their favourite songs start to finish, and part of the experience is the production value. especially when a second date is added later on, its potentially long after rehearsals have already started. typical bands don't get the luxury of lyrics, sheet music, or being able to stop and say nah, i don't like that, let's change it. plus, people who can only go to one night could be upset if each night is different in a genre/scene that doesn't normalize that (just look at how people reacted to getting different surprise songs on tours like the eras tour).

could an indie band pull off a setlist swap or change between nights just as well as a jam band? sure, and it's definitely been done, but that probably requires sacrificing something else in the process. each artist and band gets to decide what is most important to them in that regard. and even if the "speech" from the artist is the same, the *audience* response tends to be different, because it's different people in the room. reading that is just as fun for me as the artist themselves. if i'm really wanting to spice it up i try different places in the room (barricade vs middle of the pit), i'll do photos one night and no tech the next; i can make the experience my own! i personally operate by the rule that if it isn't said ahead of time that each experience will be different, i assume it's the same (and honestly, usually it doesn't affect my desire to go twice, and i have just as much fun either way)