Why would probate be posted at the court house?

It could very well and likely is a state statute requirement. Ask in the probate court office.

A more complete overview:

https://ez-probate.com/learn/blog/are-probate-records-public/

Probate is a matter of public discourse. Thats why some folks seek to avoid it. .

Once a Will is probated it too becomes public knowledge. As said posting info makes creditors and interested parties aware that an estate is now in probate. They can then file so they get payment or contest the Will.

I know a family that a brother, who was executor refused to give certain beneficiaries their share. By making the Will public, they can see that they are beneficiaries and sue for their share.

Creditors can make a claim on estate. It’s part of courthouse public records. If someone thinks they are an heir they can turn their name or if someone objects to the person named executor they can say why they don’t think the person should be executor. As Pam Z wrote, they are also published in the newspaper.

Ours are posted in the paper, so any creditors can make a claim

Bulletin board at my local courthouse posts which estates have been filed, who the executor is and dates for final filings. It’s public information.