OK, let me take both questions:
1. AM radio built out in the 1920-40's. It started on the west coast and northeast, where the population density was and is greatest. Hence, there were a lot of stations on in the northeast by the time the southern stations got around to applying for a license. WWII also interrupted things. There was also a lot of frequency swapping and reallocations going on as well back then. Therefore, most southern stations had to protect pre-existing NE stations. That's also why you find most of the big old AM's transmitters out around North Memphis...back then they were located well outside the city limits, and covered all of the city at night.
Example: 680 AM was originally on 1240. They applied for and got 680 10Kw day and 5KW night in 1939...but it didn't get built until after WWII because Rosie the riveter was building war stuff instead of new phasers and transmitters. I happen to know this because I found all that paperwork one day while we were cleaning up out at the 680 transmitter site around 1982. By 1944 stations in Boston (WRKO) and Charleston SC (WPTF) were already on the air...so WMPS had to protect them. The 680 pattern also protects what was once KFRC in San Francisco, I think.
2. We don't have non-DA 50 KW stations because most of the bigger cities got them first, or had backers with more political clout. Also, WLAC is not the powerhouse you think it is. 50KW, yes, but highly directional. 680 still puts a good signal down to the gulf coast on a good night.
1. AM radio built out in the 1920-40's. It started on the west coast and northeast, where the population density was and is greatest. Hence, there were a lot of stations on in the northeast by the time the southern stations got around to applying for a license. WWII also interrupted things. There was also a lot of frequency swapping and reallocations going on as well back then. Therefore, most southern stations had to protect pre-existing NE stations. That's also why you find most of the big old AM's transmitters out around North Memphis...back then they were located well outside the city limits, and covered all of the city at night.
Example: 680 AM was originally on 1240. They applied for and got 680 10Kw day and 5KW night in 1939...but it didn't get built until after WWII because Rosie the riveter was building war stuff instead of new phasers and transmitters. I happen to know this because I found all that paperwork one day while we were cleaning up out at the 680 transmitter site around 1982. By 1944 stations in Boston (WRKO) and Charleston SC (WPTF) were already on the air...so WMPS had to protect them. The 680 pattern also protects what was once KFRC in San Francisco, I think.
2. We don't have non-DA 50 KW stations because most of the bigger cities got them first, or had backers with more political clout. Also, WLAC is not the powerhouse you think it is. 50KW, yes, but highly directional. 680 still puts a good signal down to the gulf coast on a good night.