It did not always hold true, but when analogue television originally began in earnest, the first television station in an major market area usually got the lowest channel.
This comes to mind as we celebrate the 60th anniversary of many of the early stations. In Edmonton, it was Channel 3 and Calgary Channel 2. CBUT-TV was Channel 2 in Vancouver and was B.C.'s first licensed station; KVOS-TV in Bellingham was actually on the air first, and Vancouver residents had been watching Seattle TV before that.
Seattle's first station, which became KING-TV, was assigned Channel 5 in 1948.
An interesting exception is KATU-TV in Portland, which got the City's last available VHF channel when they signed on in 1958, and was assigned Channel 2. Why? My personal guess is that Vancouver was originally considered too close for two full power stations to co-exist without interference. And I do remember watching Jack LaLanne's syndicated show quite clearly on KATU before CBUT signed on in the summer when conditions are better for regional skip. This from a Burnaby location with no line of sight to the South.
Lower channels were better, delivering a better signal for less power. In fact, the first TV stations were on the air before the U.S. entered World War II, and were assigned frequencies around 42 MHz. TV as it existed after the War began on Channel 2 around 55 MHz. It was not so much that the lower frequencies were needed for other things, but that Shortwave Skip was a bad thing, causing interference, and even a small amount of interference really played havoc for a received television picture.
There is a big gap between Channel 6 and 7 for FM and commercial (taxis, etc.) use, and a smaller gap between Channel 4 and 5, which explains why KOMO-TV and KING-TV could co-exist in the same market. In the early years, there was a major OTA reception benefit to being on Channel 6 or lower, and early stations really pushed to be there.