2 big problems for them. 1. 烂泥扶不上墙。2. 上梁不正下梁歪。Seriously, what is wrong with the governance of Pakistan and Sri Lanka?
If this keeps on going, Western and Indian propaganda machines are going to work 24/7 against China and the BRI in the region. This situation isn't going to do any good for China.
Besides, the more countries that defaulted, the more countries that would become slaves of the American imperialist tool i.e. IMF. Sri Lanka is a prime example.