"Puri" specifically means "to be clean" (it is the verbed form of "pura"), so you need to add the affix "-ig-" to make it transitive. In other words, "-ig-" is a suffix used to denote making something the quality of the root which you have attached to it.
It says my translation "He used to clean the whole space." is wrong because it should be "He has cleaned the whole space." If that's correct, what would be the correct way to say in Esperanto "He used to clean..."?