If it's essentially a growth round labelled as an A you can normally negotiate the vesting schedule, but if you're at a standard Series A point, then it's unlikely you'll be able to change it unless you're a super hot deal.
It'll likely take 7+ years from a Series A to an exit, if a founder leaves straight after funding and keeps all their equity, that's hugely demoralizing to the rest of the founders. They'll have to do the work to generate the value of the business over the next decade and end up with exactly the same rewards as the founder who left. It's the kind of thing that kills businesses.
From an investor perspective, an investor is unlikely to want to invest if the founders aren't committing to stick with the business.
It'll likely take 7+ years from a Series A to an exit, if a founder leaves straight after funding and keeps all their equity, that's hugely demoralizing to the rest of the founders. They'll have to do the work to generate the value of the business over the next decade and end up with exactly the same rewards as the founder who left. It's the kind of thing that kills businesses.
From an investor perspective, an investor is unlikely to want to invest if the founders aren't committing to stick with the business.