Ask a landlord-tenant lawyer and get answers ASAP
Hello and welcome! My name is ***** ***** I will try my level best to help with your situation or get you to someone who can.
First, I agree with you wholeheartedly that they should replace the carpet since you have been such a good tenant..
But legally they have no obligation to do so unless it says they will in a written lease or it has become dangerous (like a tripping hazard due to frayed areas). The reason they won't replace it is money....they get no more money from you with new carpet than with old. So them spending $1000 on new carpet only would benefit you, not them. They don't realize any benefit, only cost, so they won't replace it until they absolutely have to...which is when they are trying to lure a new tenant in after you get fed up and move out.
It isn't fair or right... but it is how many landlords act. Every day that they can keep a dollar in their pocket instead of spending it is a win for them.
I am very sorry that I don’t have better news, but please understand that I do have an ethical and professional obligation to provide customers with legally correct answers based on my knowledge and experience, even when I know the answer doesn’t make the customer happy...