The main problem is that most people who want to analyse daily or weekly data want to do something like use a frequency of 365 days per year or 52 weeks per year but the number of days or weeks in a year is not 365 or 52 or even constant. If you drop one day in leap years in the case of daily data, say, or use 7 days for each week of the year except one which has 8 or 9 days in the case of weekly data, say, then you can fudge it. An endless variety of schemes is possible.
Read through this thread for an example.