Question

Witches have been executed since the beginning of time yet haven't been since 1811 in any way that I can understand,?

Answer 1

it ended because home nations were able to assert more authority over colonies.

Answer 2

It seems some people were accused of being witches and were executed in some countries of Africa even in 21st century.  

In 20th century also there had been some incidents like that in some parts of India and in Africa. Perhaps else where.

Perhaps they are not so well documented or publicised.