In some places the line sits on geology that is prone to causing "wet spots" that effectively make the track ride bumpy. This in turn means that drainage and ballasting has to be renewed quicker than in other parts of the country. The section from Shenfield to Colchester, in places, is particularly bad.
The overhead line equipment was installed at various intervals from just before World War II to the late 1980's. The WWII vintage wiring wasnt tensioned with weights so needed replacing due to age and sagging issues in the heat and the 1980s wiring kit was/is cheap and nasty.
A lot of signalling needed renewing over the last 10 years, namely the Marks Tey/Colchester area to Thorpe-Le-Soken and Walton. You've also got the S&T renewals going on in deepest Norfolk right now, to replace old semaphores.
As an aside, Clacton station throat and depot was missed off as NR run out of money. There are still some interesting LNER style search light signals here and the ageing signal box is still functional with its mechanical levers, so I guess in time that will get replaced too.
It's a heavily used railway carrying loads of freight and high intensity passenger diagrams. It really does need a lot of TLC.