Ninja either gets the data from another source or if from IB, then they are either not getting 1 minute data (5 minute data could be retrieved for longer periods) or are making multiple requests.
I cannot speak for Ninja about their design decisions and target audience, but for QT and for MT, the ability to backfill more than a handful of charts without having to wait 10 minutes trumps the higher # of days, particularly when
1) QT/MT stores whatever it gets, so it will have more data as days go by
2) you can use other datafeeds like IQFeed to backfill.
MT will be able to backfill 10 days using IB. 60 with IQFeed