If we want to establish a long term presence in space, we want to use rotating habitats to approximate the forces gravity places on the body. For these to not nauseate the human body, they need to be fairly large which is part of why there has not been any such stations built yet (another is scientists are obviously more interested in the effects of micro gravity than of something that already exists on Earth). Rocket launches are dropping in price sharply in recent years though and space tourism is likely to grow exponentially starting this year and out (there are already more civilian launches scheduled for this year than there has been since the space age started combined).
One question which we have no idea about is what are the effects of low gravity on the human body. There have only been 24 people who have visited the moon (only half of which walked on it's surface) and none of them stayed for longer than a few days. We don't know if the Moon's gravity is more than enough or if Venus's gravity would still too little. If the program does not burn into a fiery heap from a corrupt congress and Boeing, the hope is that the Artemis program may begin answering these questions.
I completely agree with your reasons why it hasn't been explored further (sadly budget issues killed even a small experimental module for the ISS[1]). Just how large is somewhat disputed though[2, pages 20-22]. By these estimates, ~10 Starship launches (ballpark $100M-500M launch price tag) could loft a dumbbell-shaped rotating station into LEO.
1: https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Modu...
2: https://space.nss.org/wp-content/uploads/Space-Settlement-Po...
With space and robots we're very much in the situation "parents sending off their children to explore the world but unable to leave the village themselves."
Even assuming that we can't use mirror arrays to use natural lighting within habitats like O'Neil envisioned, there is nothing about sunlight that we cannot replicate with artificial lighting. In fact, we could make a safer substitute that forgoes the ultraviolet radiation.
It also doesn't take that much radiation shielding to do a better job of protecting us against cosmic radiation than the Earth does. While there is 100 KM of atmosphere between us and the vacuum, that is air and of a density that drops sharply with altitude. We could easily match and exceed that protection with plating of about 20 metres.
The reason why radiation is such a concern in space travel at the moment is because current launch costs prevents any but the most spartan kinds of shielding from being economically viable. Once we can construct launch assist devices like rotavators and orbital rings, that is not going to be a major limitation anymore.
If there were an important reason to move faster, they would have built something different.
It is difficult to overstate what a limitation this has been for research there. Even without the benefit of a vehicle, a human walking at a natural pace would over a year be able to cover a larger region than all of the previous rovers sent combined across their entire lifetimes.
With fewer constraints, they would have built something different.
Even if we don't bother landing humans on Mars, it would still be very useful to have some in orbit to be able to have a real time feed on the ground as opposed to anywhere between the 3 to 22 minutes (one way!) delay that it is from Earth. While our automation is getting better, it is nowhere close to matching that of a human scientist for at least several decades yet.
There are some mild improvements to autonomy. Apparently this rover is somewhat more self-driving? The helicopter apparently won’t do much, but maybe on another mission it will.