While there's almost certainly an element of "let's get this done and over with before the push to switch out Biden grows even larger," Jamie Harrison's explanation[0] would suggest that there's still a very real legal concern behind the push. Specifically, this little nugget[1] from the Ohio Constitution:
> [...]No law passed by the general assembly shall go into effect until ninety days after it shall have been filed by the governor in the office of the secretary of state, except as herein provided.[...]
So while Ohio eventually passed a law that would extend the deadline to avoid the original problem, because it wasn't done passed as an emergency law not subject to referendum[2] since that would have required a 2/3 majority, that law doesn't actually go into effect until 90 days after its passage.
In other words, the law changing the notification requirement from 90 days prior to a general election doesn't actually go into effect until 90 days after its passage...which is after the original notification deadline. It might seem like a technicality, but it all but guarantees the issue will have to be litigated and there's a significant possibility Democrats would lose the case in that case. Risking the possibility of Biden being left off the ballot as a result would be an absurd dereliction on the DNC's part.
0. https://x.com/harrisonjaime/status/1813241706990473389
1. https://codes.ohio.gov/ohio-constitution/section-2.1c
2. https://codes.ohio.gov/ohio-constitution/section-2.1d
