You couldn't make this up!

[#1]

Regarding the Upload, the BT estimate 3 years ago was 10.9Mbps for my line, the best I got was around 9.5Mbps but this has fallen to it's current level in that time and the estimates have also been dropped, easier for BT and OR to do that than provide more capacity and giving you the rates you originally signed up too. The rates have even fallen in the time I've been with PN but as far as Upload is concerned no one wants to know if your speeds are outside the estimates, mine border the min FTTC A (Clean) range and sometimes drop below it but it falls on deaf ears.
The strange thing is it dropped some 3Mbps when everyone started selling BT TV, stealing from us to cater for the goggle box brigade maybe?

[#2]

Or people further away from the cab signed up for FTTC, which would increase the amount of Upstream Power Back Off (UPBO) required for everyone closer.

[#3]

Maybe I was one of the first if not the first to sign up on my cab.

[#4]

The max and min estimates from BT wholesale are 80th and 20th percentile respectively for your address area.
Most isp's I am aware off use the clean 20th percentile figure for their estimates (so basically already been conservative), so to then use a even lower speed as a fault threshold is extremely conservative, basically the fault threshold is deliberately set low to reduce fault costs.
This situation has came about for a multitude of reasons but the key ones I think are.
1 - a user base that thinks price is everything so always haggling for retention deals, hopping isps etc.
2 - because of #1 CP's likewise only care about low cost so accept poor service from openreach for lower costs.
3 - Openreach been very inefficient and ran badly, resulting in high prices for poor service.    They are very hostile to fixing/replacing copper issues (which is easily explained by the fact replacing copper an obselete technology with more copper is dead money) whilst bleeding that same copper dry for revenues as long as possible.