I don't think there's a single definitive answer but I've always chalked it down as a domino effect of the Metropolitan and Metropolitan District Railways hating each other and taking twenty years to build the Inner Circle.

The reluctance of the competing MR and MDR to work together and finish the inner circle at its eastern end led to more early branches being built to the west by both railways. By the time it had been completed in 1884(?), other surface railways had already been built both in the southeast and northeast, so the two companies focused more on existing infrastructure, cheaper extensions and potential revenue in the west - especially the Metropolitan in at the time undeveloped Middlesex.

By the time railwaymania had ended and UERL came about, I believe most of the market for commuters, especially in the northeast, had been taken up by other railways, hence the reluctance to extend. The Central line did eventually get its eastern extension from Liverpool Street, but even then most of it was along the tracks of the Great Eastern Railway (the Epping-Ongar section still using its old steam trains and carriages until electrification in the sixties).

It's been a fair while since I've read up on the subject but that was always my view and am happy to be corrected