The company paying means the company has a strong incentive to minimize how much of it is used. They don't really receive any benefit for paying out leave, it costs them a lot, both financially and in terms of work done. It creates strong incentives to discriminate against people who might take the leave in hiring process, to subtly retaliate against people who take leave, and so on. (Yes, all those are illegal, but proving that a hiring manager is doing so is next to impossible in all but the most egregious cases)
The whole "people might not come back" thing is just another instance of the misaligned incentives. It's probably good for society if we have people raising their own children, but it's bad for the employer who is currently expected to pay leave.
We should take all of this entirely out of companies hands, run it through taxes and the government (leaving the general payout scheme unchanged). It would remove the worst of the misaligned incentives (now at least companies aren't paying someone who isn't producing value for them) and should come at minimal cost (you'd have to worry more about fraud, companies and people conspiring to get more leave than they are entitled to).