Why are so many 'New' episodes broadcast out of order for the 'Series'?

None of my fav shows have started yet to be able to tell about recording order. But what MrSL says happens with rerun series when there is a marathon run. Of course the guide does not tell you date or episode number until until you go to details. Just checked a series marathon and it is all over the dates first run and not a week apart consectively. You would not know until recorded