Mission creep
(What's with the "meta-data" rubbish in the headline? Its data. Actually, its like having a CCTV camera pointed at your screen all the time, but which can't see the actual user. Only its less a bit less accurate than that.)
As you increase the age of data you decrease its reliability and usefulness.
IP source/destination & port numbers might be fine for today's data. What happens when it was two years ago? Who was living at the house? Now you need to keep name/address/account data as well as the traffic data. So you have another privately-held database to complement the land registry. This isn't current data, this goes back... forever?
That kiddie porn that was accessed - was the house owner's owner's daughter back from college for that weekend? Did she use Dad's computer? Has the disk or the laptop been changed, so you can't tell who had access? Is the Mr Sayeed who was living there seven years ago the same Mr Sayeed who is there now? How about the house-share full of college students? Can you track them down, do you even know if the people on the rental agreement are real ones who were there? Even for phone data - did Ms Sayeed use her Dad's phone to call her zealous boyfriend? Did she use it as a hotspot?
The thing about "digital footprints" is that they might be accurate enough for ad-slingers, but they aren't anywhere close to accurate enough for legal purposes and the further back you go, the more difficult it is to see the unknowns and the easier it is to make assumptions.
"Don't tell anyone your pin" is all well and good, but its hard to use a phone a lot and have a pin no-one has seen, even if they aren't looking. If they are trying to cover their tracks by secretly using your kit, its pretty hard to stop them. Its your phone, its been "secured" and you were in the house. "It wasn't me but I don't remember who it could have been" will be difficult to pull off, if you look suspicious.
We haven't even begun to look at what happens when websites move addresses.
The data shouldn't be collected because it is often misleading. That doesn't bother advertisers and (other) criminals who don't care about failures or historical accuracy and for whom a scatter-gun approach is valid. The longer you store it, the worse the situation becomes so you need more data to try to keep it accurate, but still, as events fade from human memory, the data becomes more and more misleading.
Biting the hand that feeds IT
