I assume then that an employer could hold a potential hire accountable for damages if the candidate backs out of the job offer/commitment after agreeing?
If two people sign a paper agreeing that they would both do something on a future date, it's generally a contract, and they don't get to back out of it without paying some form of compensation.
The difficulty of job offers is that you generally can't force the employer to continue hiring a person they don't want, so the most you can get is severance assuming they fire you on the first day at work.
As for whether the employer can sue if the potential hire backs out... my understanding is theoretically yes, but probably the only thing you can claim is the amount they would pay if they resigned without notice. Which generally isn't worth the legal costs and the PR risks.
Don't get me wrong, the employer can then fire the employee within the probation period of two weeks scotch-free (well, after a bunch of paperwork), and the employee can quit within that period as well, and while it might seem the same it's not because that triggers all sorts of gvmt protections for the employee (mainly, unemployment benefits, but YMMV).