@Philip C., thanks for reaching out. Our MLS access (at least in California) is limited to the association we are members of. There are "datasharing agreements" that allow our listings to be shared automatically with other regional MLSs and vice-versa. For example, we share with Ventura, San Fernando, Pasadena, the Antellope Valley and all the way down into Orange County. It's called the CRMLS or California Regional MLS. More information can be found here:
https://go.crmls.org/coverage-area-map/
Now, we can look at the rest of the country through the same sites as you, realtor.com or any of the other portals out there. The only downside is if we want to write an offer on one of those homes, we would need to find an agent out there to do the paperwork and handle the transaction. You have to be licensed in each state you do business in.
Long story short, if I wanted a house in Dallas, I'd have to call my friend Richard out there to walk me through the process and write me up a contract, even if I found the house online and even though I'm a licensed sales agent in California.