Help!!! having to cover TWO consecutive maternity leaves of two colleagues in a 3 person team

Does anyone feel that companies should TRY to get maternity leave cover or try to factor this into productivity?

Ive had to cover 8 months worth of work for two different colleagues. It's highly unfair to have to cover for people when it doesnt even benefit me... if anything it gives me stress and reduces my own ability for nation building.