Accounts Installed vs Sales Activity

I have a monthly subscription channel
(and no test users)

I find that there is a very big difference between the accounts installed number
and the number of sales

on a channel that just got published a couple days ago--
sales activity is showing about 50% of the accounts installed..

and on a channel that has been live for some months...
sales activity is showing about 30-45% of accounts installed...


meaning if my channel is showing 100 accounts installed
then sales activity will only be showing 50 sales..


can someone please explain this to me..

thanks