Re: What's causing this!!!
That thin soft plastic arch liner has never worn threw that tyre!
I would say the liner is loose and catching on tyre and tyre is wearing away the liner.
Your tyre is well worn across the whole surface just worn more on inner edge, you could do with four wheel alignment or your new tyre will also wear unevenly.
If you take car for a four wheel alignment you'll need a good garage with proper equipment or they will fudge figures to look like they have adjusted it and when your tyre wears unevenly again the will say you've curbed it or been down pot hole.
You can sleep in your car, but you can't race your house.