Here's a link that explains the process, starting on page 19. From the way that reads, everyone wishing to host has to go through the application process.
http://www.ncaa.org/sites/default/files/2018D1MBA_PreChampsMan_20180214.pdf
Here's the first paragraph of that section for those who don't wanna click:
"Any institution or conference interested in hosting a preliminary round of the 2018 NCAA Division I Baseball Championship must submit a proposed budget, facility evaluation form, key contacts form, proof of insurance and video board questionnaire (if applicable) to be considered to host. A separate proposed budget and key contacts form must be submitted for each round that an institution or conference is interested in hosting. Please respond to sport-specific questions and ensure the institution’s key contacts and facility information are up to date via the Championships Bid and Host Profile portal. To submit a bid, first search for the desired championship under “championships available for bid” and select “add bid.”