We just never got around to it. In practice, it turns out most well written programs with large data try not to insert one byte at the start of the file. For example, take your large Outlook "pst" file (commonly 1 - 4 GBytes). When you get an email, it seems to append it to the END of the pst file, plus update some internal tables. So a large amount of that won't change.
Also, the worst case is it wastes space in our datacenter (and some bandwidth) for 30 days and then is cleaned up anyway, so you can measure the theoretical amount of money to save and it won't profoundly change our business so we put it off. Not to say ANYTHING is off the table, we're just always swamped with some project or other. :-)
We just never got around to it. In practice, it turns out most well written programs with large data try not to insert one byte at the start of the file. For example, take your large Outlook "pst" file (commonly 1 - 4 GBytes). When you get an email, it seems to append it to the END of the pst file, plus update some internal tables. So a large amount of that won't change.
Also, the worst case is it wastes space in our datacenter (and some bandwidth) for 30 days and then is cleaned up anyway, so you can measure the theoretical amount of money to save and it won't profoundly change our business so we put it off. Not to say ANYTHING is off the table, we're just always swamped with some project or other. :-)