Because you were only mining for the first 10D and after that, you need to pay electricity fee for another 10D or more. It's not recommended because even if you 100TH, you still need to pay the electricity day by day to them. I think it's not worth it because I think they are not transparent to explain to the customer.
If you want to withdraw for 0.001 btc, you need to change the pool into btc.com so you can be able to withdraw 0.001 btc and not 0.01 btc.
That is what I can understand. Still, they are not worth.
You don't need to change to btc.com to withdraw. The mininum payout from antpool is also 0.001btc.
You can check their FAQ:
https://bitdeersupport.zendesk.com/hc/en-us/articles/360023375292-How-to-Change-the-Mining-Pool-%E5%A6%82%E4%BD%95%E6%9B%B4%E6%8D%A2%E7%9F%BF%E6%B1%A0-