1) Pre-WWI, there was absolutely no standardization in tracks and they came in an od assortment of lengths ranging from 200 yards to 600 meters. There really wasn't a heck of a lot of standardization in rules until the IAAF was formed in 1912. Sometimes there were ropes separating lanes, sometimes not. Sometimes there weren't even lanes -- imagine what it was like to get stuck on the rail in the 220y! Championship meets had at times been held on rectangular tracks or even just around stakes set in the outfield of a baseball field. For the long jump, competitors picked where they wanted the competition held and they'd turn over the turf & topsoil to make a pit. Even as late as 1962, Snell ran a WR on a grass track, which was just a 385-yard loop around stakes set in a rugby pitch.
2) The imperial distances were used because the Brits invented the modern sport of track & field in the early 1800s, and they stuck for events where it made some kind of sense because they happened to rule most of the world at that time. The Olympics went with metrics because they were invented by a Frenchman and started off fairly Euro-centric.
3) There were no standard distances beyond 1 mile until the 1930s. The US and Canadian championships had 2-mile and 5-mile races; the English championships had 4-mile and 10-mile races; Australia had 3 miles; most of Europe had 5k and 10k races. It wasn't until 1932 that pretty much everybody agreed on 3M/5k and 6M/10k.
4) Events developed in the UK or USA are imperial. Examples: men's shot & disc are 16 lbs; the men's high hurdles are 15y from the start to the first hurdle and 10y in between. Events developed in Europe are metric. Examples: the jav is 800g, the men's disc is 2 kg, and all the women's throwing implements are metric as are the distances between hurdles in both the 400H and the women's 100H.
5) And the marathon is such a screwy distance not just because they made it that distance for the 1908 Olympics, but because right after it the principal players in that race staged a series of highly publicized (and heavily wagered) professional matches which recreated the exact distance. Some of them were at the Polo Grounds in New York, and if you think a marathon on an outdoor track is bad enough, others were INDOORS at Madison Square Garden.