Hackbridge & Mitcham Junction platform extensions - or lack thereof

[samxool]

So, the platforms on the rest of the lines for all other stations other than Hackbridge and Mitcham Junction are 8 carriages long.
At Hackbridge and Mitcham Junction, they are 7.5 carriages long. This already creates the silly situation that you cannot board on the last carriage at either station (on southern trains, fcc still let you).
Now that 10 coach trains have started running on this line, all the other stations have been upgraded to 10 coaches long, but mitcham junction and hackbridge stubbornly remain short, and now the last 3 coaches you cannot alight from at these stations.
what gives? Both have plenty of flat land to extend their platforms. Carshalton has has had its platforms extended despite being on a viaduct.
It confuses me as i cannot see any reason why a) they would have short platforms before 10 coach trains, and b) post 10 car trains, whilst virtually every other station has had their platforms extended, these 2 still remain short!
I live equidistant between these 2 stations, and cannot think of one good reason why they are persistently missed out.

 

[mister-sparky]

Well Mitcham Junction has the road bridge and curve north at one end, and the descent and curve south at the other end.

 

[samxool]

Well Mitcham Junction has the road bridge and curve north at one end, and the descent and curve south at the other end.

Still plenty of room for platform extensions to the south

 

[westcoaster]

So, the platforms on the rest of the lines for all other stations other than Hackbridge and Mitcham Junction are 8 carriages long.
At Hackbridge and Mitcham Junction, they are 7.5 carriages long. This already creates the silly situation that you cannot board on the last carriage at either station (on southern trains, fcc still let you).
Now that 10 coach trains have started running on this line, all the other stations have been upgraded to 10 coaches long, but mitcham junction and hackbridge stubbornly remain short, and now the last 3 coaches you cannot alight from at these stations.
what gives? Both have plenty of flat land to extend their platforms. Carshalton has has had its platforms extended despite being on a viaduct.
It confuses me as i cannot see any reason why a) they would have short platforms before 10 coach trains, and b) post 10 car trains, whilst virtually every other station has had their platforms extended, these 2 still remain short!
I live equidistant between these 2 stations, and cannot think of one good reason why they are persistently missed out.

Hackbridge you could extend the down platform no problem (extend towards London) the up platform would be harder as there is an access point and signal in the way London end and a road bridge county end.

Mitcham junction is also a hard one even more so than Hackbridge as the platform would be on an s- bend no matter which way you extend and will cause massive sighting problems for dispatch and train platform interface.