It's not so surprising really that the most popular music is the kind of stuff that you don't really notice and is used for background music. Anything too clearly sitting at a point on the spectrum away from the middle ground would not have the mass appeal. For example I could list half a dozen folk songs that I love from this period but just the word folk would turn a lot of people off, they may prefer hard rock, but we would both be able to sit in a pub with the above playing in the background and barely have an opinion about them.
it's onot only radio play/ music channells etc. songs like "had a bad day" or "chasing cars" may have gotten a lot of play when they were flavour of the month, but where they have shot up the "most played" list is commercial/media. they lend themselves to use in adds and tv shows/movies. so every coffee/hot chocolate/fast food/ chocolate/sweet company has a ready made add for them thanks to that song. show someone have a shitty day then as the up beat chorus kicks in, show their husband/wife/child give them a bigmac/horlicks and everything is ok again, done and dusted. these then get played about 50 times a day if the company is big enough, without anyone actually requesting it.