Yes there are a lot of emotions around this and it is a complicated problem for management to solve with limited resources and pressures to keep headcount down - but part of that complication is that maternity leave isn't the only area where this comes up. Pinning this just down to maternity leave and women coming back part-time after having a baby is erasing part of the complexity, especially with an aging workforce and how contracts have changed over the years.
I work with mostly women and we have the opposite problem - we've little issue with mat leave, but we do have the retirement day dropping issue. Pretty much everyone over 50ish are on older and much better contracts and nearly all of them are part-time and most have their non-working day on either Monday or Friday, leaving those days to be particularly difficult. Somehow most of them have it so they only have to work their base site so all work at other sites is on the rest of us and they're not required to train to cover multiple roles as has been standard for years.
It's great for them. It's still sometimes frustrating when they drop down another day, I know there was some resentment when someone else got Fridays off when so many already have it or when someone has been hired that is transferring from another site that already has Friday or Monday off, but it's not at the person with the non-working days. It's confusion and resentment towards management - most who are also on those better contracts - making those choices.
With mat leave, there is at least a run up and IME there are discussions openly had even when we know they could end up changing - and all the ones where I work are covering multiple roles and most work multiple sites even at 3-4 days a week. With the heading towards retirement day dropping, no one discusses it until it's announced in the staff update emails and we're all left figuring out how we're going to cover all the needed tasks. Local management is at least willing to help cover the lower grade work, when they're not having a non-working day or leave themselves. The upper management making the decision doesn't seem to care.
And that's before, as others mentioned, those needing sick leave or similar, which is going to become a larger issue with an aging population and retirement ages going up.
A question for all those saying 'it's a management issue', which I do agree with by the way - are you saying that in your workplace, there is actually proper maternity cover? For all jobs, including where the person taking leave isn't someone who's job is easily picked up in a few days/weeks at most? How does that work?
Mat leave is generally covered okay where I work, but it's within a place where there is never proper staffing on all teams. The higher management send emails about how great it is for tech to reduce headcount (I'm not sure they understand how that impacts the lower grades whose numbers are being cut) while we go in cycles with maybe one of five teams having enough to cover the others, then something happens and that team goes down and the scrambling begins again, management is calling everywhere in the region for cover, lower grade staff gets trained on or encouraged to train ourselves on higher grade work to get it done, more agency staff come in starting to cover only the most basic, essential work that can be taught in weeks as long as they can shout over the desks to the rest of us when something new comes up while the rest of us keep things afloat, slowly building on the new person's training - if they don't leave or get fired first - until local management can finally get budget from on high to properly hire more staff in one area which covers for the rest until it all repeats.
Women having babies or even reducing workload after having a baby or before retirement is not why we're scrambling so much. It's not even typically a local management issue. It's an upper management 'vision' to keep down headcount and put as much as possible on people being paid the least while it works, then give us platitudes about us all working together when it breaks. While all the emotions are normal, being resentful at my coworkers isn't going to help that.