According to my memory this was instituted prior to the new admin team. There was a period where there were frequent issues with TOTV with performance and down time.
As the folks in charge were trying to fix the issue, I suspect by upgrading DB servers hardware and software, they also instituted this wait.
Searches require a DB query and puts a stress on the DB servers. If too many searches are occurring simultaneously the servers may not have the capacity to handle. It is not just new posts, it is any search.
Do not read this as fact as my memory is often 'based on a true story'.