You have absolutely misunderstood.
I think quite a lot of people have told you that there is usually a set limit on vet expenses. Not a single person has told you the lessee has to have an open checkbook. The person leasing doesn’t pay all rehab expenses for ever and ever as you seem to think despite all the explanations. Using the owner’s farrier isn’t an advantage that deserve a break. People have been quite clear about that. That is what is aggravating, that you keep not understanding that. Honestly if you don’t agree to the terms of most leases then buy your own horse.
As I have explained to you, the people leasing my horses pay for their board/feed, foot care, shots and coggins, injections, and any minor emergency care. If the horse is lame then I expect them to let me know the vet is coming out and let me know what the vet decided. If it’s something like an abscess then they would pay for it. If it’s something like a bowed tendon then once they’ve diagnosed it the lease ends and the horse comes back to me. The lease contract has a set max of the horse value if for example the horse dies in their care due to neglect. They aren’t paying me on top of that.