The applicant accepted your job, but now all the other places he/she applied are starting to respond, and invariably, at least one will be a better deal.
Early in our marriage, after an exhausting *we will get back to you in several months* job search, my wife quit a newly accepted *Pay the Bills* job because her *Reach* dream job she had applied for finally called back and made a terrific offer. I had to heavily encourage her to quit the Pay the Bills position, loyal-minded as she can be. Years later, that good choice has been obvious.
Look out for yourself, because hierarchical soul-less e n t i t y will not!
Hiring employers should show a lot of love those first 2-3 months to deflect other tardy offers from the applicants job search. It takes that long to see if your new hire is not a *touch and go* to a better choice.