Why doesn't Windows iTunes keep all iPhone backups, and does it overwrite recent ones?

So I was trying to restore my iphone to a previous backup, which I made most recently about 2 weeks ago. When I went back it only shows the last backup from 3 months ago and the one it just made automatically when I plugged the phone in.

I then did another backup and it seemed to over-write the one from just a few minutes before.

So my questions are:

1. why doesn't windows itunes keep all of the backups from iphone? There are definitely ones missing because I backup before every IOS update and they aren't there.
2. does it over-write backups that are made within a timeframe? Such as the one that I did only minutes after another and so the one minutes before is no longer visible.

Note: I do backup to iTunes because I don't want to pay the exorbitant costs for iCloud. I haven't moved to Device Manager yet because that just sounds like days and days of pain for my personal (not Apple) music library.

[Re-Titled by Moderator]