Ethics. I mean, yes it's "only" mice, but still - there is no point in letting them develop into animals that can actually feel harm for no purpose, at least not until the feti are similar in development quality to naturally grown feti.
It’s often money. I’d run dozens of experiments, but some reason Forbes top 100 don’t want in the queue in front of the lab.
But also, there might be lack of results beyond that time point.
Most likely didn't work after 8.5 days
Mercy.
This work was done in mice. These are mouse embryos.
It is up to one's empathy, but mercy isn't something strictly directed towards humans. For some people it is universal, others have no mercy even for fellow humans.
Not saying they’re the same but humans essentially look like fish, chickens, pigs (gils, tails, etc) for the first few weeks.