Even in cases where I told them I broke a piece in a kit, they didn’t seem to care and it looked like the kit was going right back into stock to me.
Parts store do it because it gets you in the door to buy parts. If the lending was done through the mail, I’m sure Amazon would sell more parts, but it’s not clear it would be enough more profit to cover 2-way (or 4-way if a tool was broken) shipping on the tools.
https://www.brunswicktoollibrary.org
It's pretty cheap (AUS$85/yr), and AFAIK they have about 400 members. Though Melbourne is currently in a coronavirus lockdown so everything is closed. :(
Regarding broken/incomplete tools, (prior to the lockdown) they had a day every week or two set aside to go through and fix broken/worn tools (etc).
Seems like a good solution to the tool sharing problem, and it seems to work well for everyone.