I think generally enlightenment can be achieved by humans , whether ordained or as lay. There are many lay masters who have achieved realizations, although the majority of past masters are monastics.
It depends on the environmental conditions , practitioner's inclination and motivation.
Environmental conditions - those born in Buddhist countries will more naturally follow the monastic path. In future, we may see more choosing to practice as lay people when the teachings etc become more mainstream and accessible to the public due to technological advancement and there are more qualified lay teachers.
For some, monkhood is their natural preferred path, due to past life imprints and association. At least for now, public perception of someone spiritual or attained is still biased towards an ordained monk. Hence a practitioner may choose to be ordained in order to spread dharma more effectively due to the respect accorded to one who wear robes.It is not about wanting high status but merely a pure motivation to fulfil people's wishes and their expectations in order to benefit them most. This is consistent with the development of skilful means prescribed by the bodhisattva path.
On a cautious note, there is always the danger that without the strict discipline and holding of vows that monks have to uphold, the path of lay practitioners may not be focussed and at risk of degenerating. Even if lay people hold the same vows , who is to monitor our progress without a proper system like in a monastery.
In the history of Buddhism, although there are lay people gaining realization, these are v special and exceptional people. Do most of us have such qualities to practice amidst the distractions and strong temptations of this world we are so naturally attached to ? We must be honest and realistic.