We don't know that it's not really putting them out. We don't know if they're running tight for time after work and don't have the five minutes to swing by OP's. We don't know if it's the only time the DD gets alone with a parent during the week and they enjoy the quality time for a chat. We don't know if they're already stuck in a bunch of other lift shares for other children and/or hobbies, or if they've been burned before and swore never again.
It may well be a bit mean spirited, and they're certainly not generous. But we don't know that it's any worse than that. Supposing that it's because of some nefarious competitive spirit rather than just an overly full diary is also a bit mean spirited.
AIBU - my DD has recently started a new hobby and it seems she has a bit of an aptitude for it. One of the other families seems to have latched on to us a little, they have more experience and I think they're enjoying playing the expert. This was fine, and in fairness some of the information was very useful. However, there then came numerous requests for lifts. We genuinely couldn't help the first couple of times, but the requests kept coming so I tried to back off a bit.
The problem now is that both girls have been offered an opportunity with a regional squad. It's a fair drive away, and unfortunately the other mum now can't drive due to ill health. I know they'll expect us to give the DD a lift, but to be frank, I just don't want to. I'm busy enough with work and children as it is, and it's going to be enough of a struggle to get DD there. I just don't want to add the mental load of bringing the other girl too, especially since we're trying to withdraw from the friendship a bit.
WIBU just to not mention DD joining the squad and hope the whole thing blows over?
Again, not generous, but not malicious either. And certainly not aimed at gaining some competitive advantage over OP's daughter.
Like I said, not my world, and maybe this does happen all the time. It just doesn't seem the most likely explanation.