Why do former British colonies (the US, Australia, Singapore, HK) have stronger economies than former colonies of other European powers?

Because you are cherry picking the successful ones.

There are plenty of examples of successful non-British colonies: South Korea, Uruguay, Panama, and Chile to name a few. There are plenty of examples of dirt poor ex-British colonies: South Sudan, Sudan, The Gambia, Malawi, Bangladesh, India, Sierra Leone, and Myanmar to name a few.

There are much much more impoverished ex-British colonies and citizens of ex-British colonies than successful ones.