I totally get that. Usually I would agree that to get a pet used to something they don’t particularly like, it should be done repeatedly. But, unfortunately, rabbits are different. They are prey animals, which causes them to react quite negatively to things that don’t come naturally to them. Out in the wild they have to fight a lot harder to stay alive than a predator does. Being picked up and carried is the one thing that they hate the most, nature screams in their ear “Run fool, you’re about to get eaten!” It naturally terrifies them, it’s on a whole different level than having to endure something they dislike a little bit, like a dog having to take a bath for example. They might not like it, but it doesn’t scare the pants off of them.
Some people have had some success getting their rabbits used to being held enough that they tolerate it for a little while. But most rabbits will not get used to it. To the contrary, a lot of the time, picking them up repeatedly does nothing but destroy their trust in you, until they run and hide when a person approaches them, and if that’s not an option, they can turn and become aggressive. Sadly this is one of the reasons lots of them end up in shelters. People pick them up not knowing how much they hate it, the rabbit starts to bite, is deemed “mean” and gets dumped.
It’s just not something that they get used to easily, as it completely goes against their nature. As far as grooming and vet trips go, I think it would be a better option to teach them to enter their carrier on their own using treats, that way you won’t have to pick them up at all. Grooming could be done while they’re eating, most rabbits are little pigs and don’t care about much else if there’s food in front of them. You just have to learn what works for your rabbits and what doesn’t, they’re all individuals. But generally, I think picking them up should be avoided if possible. We pick ours up to clip his nails because there’s just no other way, but boy does he hate it…