I would suggest that it was due to his hard work bringing the true Faith to the people of that area.
Why bother if they can desire baptism from a distance? BECAUSE they needed BAPTISM OF WATER in order to enter the Church and be able to receive any other sacrament! Why did Arch. L. go to Africa? BECAUSE the natives could not be saved without Baptism of Water. The Church in her highest authority says WATER is necessary, and there is no substitute. BOD/BOB is only the SPECULATION of various saints and theologians while Baptism of Water is ABSOLUTE.
"Unless a man be born again of WATER and the Holy Ghost, he CANNOT enter the Kingdom of Heaven." - Jesus Christ